Merge branch 'intrinsic-vectorisation' into 'master'

Intrinsic vectorisation

I have implemented vectorised versions of the symmetrical and non-symmetrical density and force interaction functions for the `GADGET_SPH` scheme.

There are also tests for each interaction in `tests/testInteractions.c`.

There are some bug fixes in the `DEFAULT_SPH` along with changes to the `struct part` and minor renaming of variables.

Calculations of the `balsara` switch and `P_over_rho2` are now performed in `hydro_prepare_force()` rather than in `runner_iact_nonsym_force` or `runner_iact_force`.

Note: The !203 `gadget2-part-update` branch should be merged with master prior to this merge request.

See merge request !204

examples/main.c

@@ -269,12 +269,6 @@ int main(int argc, char *argv[]) {
 /* Temporary abort to handle absence of vectorized functions */
 #ifdef WITH_VECTORIZATION
 
-#ifdef GADGET2_SPH
-  error(
-      "Vectorized version of Gadget SPH routines not implemented yet. "
-      "Reconfigure with --disable-vec and recompile or use DEFAULT_SPH.");
-#endif
-
 #ifdef MINIMAL_SPH
   error(
       "Vectorized version of Minimal SPH routines not implemented yet. "

src/hydro/Default/hydro.h

@@ -145,17 +145,17 @@ __attribute__((always_inline)) INLINE static void hydro_prepare_force(
 
   /* Compute this particle's sound speed. */
   const float u = p->u;
-  const float fc = p->force.c = sqrtf(hydro_gamma * hydro_gamma_minus_one * u);
+  const float fc = p->force.soundspeed = sqrtf(hydro_gamma * hydro_gamma_minus_one * u);
 
   /* Compute the P/Omega/rho2. */
   xp->omega = 1.0f + 0.3333333333f * h * p->rho_dh / p->rho;
-  p->force.POrho2 = u * hydro_gamma_minus_one / (p->rho * xp->omega);
+  p->force.P_over_rho2 = u * hydro_gamma_minus_one / (p->rho * xp->omega);
 
   /* Balsara switch */
   p->force.balsara = normDiv_v / (normDiv_v + normRot_v + 0.0001f * fc * ih);
 
   /* Viscosity parameter decay time */
-  const float tau = h / (2.f * const_viscosity_length * p->force.c);
+  const float tau = h / (2.f * const_viscosity_length * p->force.soundspeed);
 
   /* Viscosity source term */
   const float S = fmaxf(-normDiv_v, 0.f);
@@ -214,7 +214,7 @@ __attribute__((always_inline)) INLINE static void hydro_predict_extra(
     u = p->u *= expf(w);
 
   /* Predict gradient term */
-  p->force.POrho2 = u * hydro_gamma_minus_one / (p->rho * xp->omega);
+  p->force.P_over_rho2 = u * hydro_gamma_minus_one / (p->rho * xp->omega);
 }
 
 /**

src/hydro/Default/hydro_iact.h

@@ -371,8 +371,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
   mj = pj->mass;
   rhoi = pi->rho;
   rhoj = pj->rho;
-  POrho2i = pi->force.POrho2;
-  POrho2j = pj->force.POrho2;
+  POrho2i = pi->force.P_over_rho2;
+  POrho2j = pj->force.P_over_rho2;
 
   /* Get the kernel for hi. */
   hi_inv = 1.0f / hi;
@@ -398,7 +398,7 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
   omega_ij = fminf(dvdr, 0.f);
 
   /* Compute signal velocity */
-  v_sig = pi->force.c + pj->force.c - 2.0f * omega_ij;
+  v_sig = pi->force.soundspeed + pj->force.soundspeed - 2.0f * omega_ij;
 
   /* Compute viscosity parameter */
   alpha_ij = -0.5f * (pi->alpha + pj->alpha);
@@ -480,13 +480,13 @@ __attribute__((always_inline)) INLINE static void runner_iact_vec_force(
   mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
                  pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
   piPOrho2.v =
-      vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2, pi[2]->force.POrho2,
-              pi[3]->force.POrho2, pi[4]->force.POrho2, pi[5]->force.POrho2,
-              pi[6]->force.POrho2, pi[7]->force.POrho2);
+      vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2, pi[2]->force.P_over_rho2,
+              pi[3]->force.P_over_rho2, pi[4]->force.P_over_rho2, pi[5]->force.P_over_rho2,
+              pi[6]->force.P_over_rho2, pi[7]->force.P_over_rho2);
   pjPOrho2.v =
-      vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2, pj[2]->force.POrho2,
-              pj[3]->force.POrho2, pj[4]->force.POrho2, pj[5]->force.POrho2,
-              pj[6]->force.POrho2, pj[7]->force.POrho2);
+      vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2, pj[2]->force.P_over_rho2,
+              pj[3]->force.P_over_rho2, pj[4]->force.P_over_rho2, pj[5]->force.P_over_rho2,
+              pj[6]->force.P_over_rho2, pj[7]->force.P_over_rho2);
   pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho, pi[4]->rho,
                     pi[5]->rho, pi[6]->rho, pi[7]->rho);
   pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho, pj[4]->rho,
@@ -496,11 +496,11 @@ __attribute__((always_inline)) INLINE static void runner_iact_vec_force(
   pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u, pj[4]->u, pj[5]->u,
                   pj[6]->u, pj[7]->u);
   ci.v =
-      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c,
-              pi[4]->force.c, pi[5]->force.c, pi[6]->force.c, pi[7]->force.c);
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed,
+              pi[4]->force.soundspeed, pi[5]->force.soundspeed, pi[6]->force.soundspeed, pi[7]->force.soundspeed);
   cj.v =
-      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c,
-              pj[4]->force.c, pj[5]->force.c, pj[6]->force.c, pj[7]->force.c);
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed,
+              pj[4]->force.soundspeed, pj[5]->force.soundspeed, pj[6]->force.soundspeed, pj[7]->force.soundspeed);
   vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
                      pi[3]->force.v_sig, pi[4]->force.v_sig, pi[5]->force.v_sig,
                      pi[6]->force.v_sig, pi[7]->force.v_sig);
@@ -530,18 +530,18 @@ __attribute__((always_inline)) INLINE static void runner_iact_vec_force(
 #elif VEC_SIZE == 4
   mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass);
   mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
-  piPOrho2.v = vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2,
-                       pi[2]->force.POrho2, pi[3]->force.POrho2);
-  pjPOrho2.v = vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2,
-                       pj[2]->force.POrho2, pj[3]->force.POrho2);
+  piPOrho2.v = vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2,
+                       pi[2]->force.P_over_rho2, pi[3]->force.P_over_rho2);
+  pjPOrho2.v = vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2,
+                       pj[2]->force.P_over_rho2, pj[3]->force.P_over_rho2);
   pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho);
   pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho);
   piu.v = vec_set(pi[0]->u, pi[1]->u, pi[2]->u, pi[3]->u);
   pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u);
   ci.v =
-      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c);
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed);
   cj.v =
-      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c);
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed);
   vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
                      pi[3]->force.v_sig);
   vj_sig.v = vec_set(pj[0]->force.v_sig, pj[1]->force.v_sig, pj[2]->force.v_sig,
@@ -637,18 +637,14 @@ __attribute__((always_inline)) INLINE static void runner_iact_vec_force(
   piu_dt.v += mj.v * tc.v * (piu.v - pju.v);
   pju_dt.v += mi.v * tc.v * (pju.v - piu.v);
 
-  /* compute the signal velocity (this is always symmetrical). */
-  vi_sig.v = vec_fmax(vi_sig.v, v_sig.v);
-  vj_sig.v = vec_fmax(vj_sig.v, v_sig.v);
-
   /* Store the forces back on the particles. */
   for (k = 0; k < VEC_SIZE; k++) {
     pi[k]->force.u_dt += piu_dt.f[k];
     pj[k]->force.u_dt += pju_dt.f[k];
     pi[k]->force.h_dt -= pih_dt.f[k];
     pj[k]->force.h_dt -= pjh_dt.f[k];
-    pi[k]->force.v_sig = vi_sig.f[k];
-    pj[k]->force.v_sig = vj_sig.f[k];
+    pi[k]->force.v_sig = fmaxf(pi[k]->force.v_sig, v_sig.f[k]);
+    pj[k]->force.v_sig = fmaxf(pj[k]->force.v_sig, v_sig.f[k]);
     for (j = 0; j < 3; j++) {
       pi[k]->a_hydro[j] -= pia[j].f[k];
       pj[k]->a_hydro[j] += pja[j].f[k];
@@ -684,8 +680,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
   mj = pj->mass;
   rhoi = pi->rho;
   rhoj = pj->rho;
-  POrho2i = pi->force.POrho2;
-  POrho2j = pj->force.POrho2;
+  POrho2i = pi->force.P_over_rho2;
+  POrho2j = pj->force.P_over_rho2;
 
   /* Get the kernel for hi. */
   hi_inv = 1.0f / hi;
@@ -711,7 +707,7 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
   omega_ij = fminf(dvdr, 0.f);
 
   /* Compute signal velocity */
-  v_sig = pi->force.c + pj->force.c - 2.0f * omega_ij;
+  v_sig = pi->force.soundspeed + pj->force.soundspeed - 2.0f * omega_ij;
 
   /* Compute viscosity parameter */
   alpha_ij = -0.5f * (pi->alpha + pj->alpha);
@@ -785,13 +781,13 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
   mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
                  pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
   piPOrho2.v =
-      vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2, pi[2]->force.POrho2,
-              pi[3]->force.POrho2, pi[4]->force.POrho2, pi[5]->force.POrho2,
-              pi[6]->force.POrho2, pi[7]->force.POrho2);
+      vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2, pi[2]->force.P_over_rho2,
+              pi[3]->force.P_over_rho2, pi[4]->force.P_over_rho2, pi[5]->force.P_over_rho2,
+              pi[6]->force.P_over_rho2, pi[7]->force.P_over_rho2);
   pjPOrho2.v =
-      vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2, pj[2]->force.POrho2,
-              pj[3]->force.POrho2, pj[4]->force.POrho2, pj[5]->force.POrho2,
-              pj[6]->force.POrho2, pj[7]->force.POrho2);
+      vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2, pj[2]->force.P_over_rho2,
+              pj[3]->force.P_over_rho2, pj[4]->force.P_over_rho2, pj[5]->force.P_over_rho2,
+              pj[6]->force.P_over_rho2, pj[7]->force.P_over_rho2);
   pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho, pi[4]->rho,
                     pi[5]->rho, pi[6]->rho, pi[7]->rho);
   pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho, pj[4]->rho,
@@ -801,11 +797,11 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
   pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u, pj[4]->u, pj[5]->u,
                   pj[6]->u, pj[7]->u);
   ci.v =
-      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c,
-              pi[4]->force.c, pi[5]->force.c, pi[6]->force.c, pi[7]->force.c);
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed,
+              pi[4]->force.soundspeed, pi[5]->force.soundspeed, pi[6]->force.soundspeed, pi[7]->force.soundspeed);
   cj.v =
-      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c,
-              pj[4]->force.c, pj[5]->force.c, pj[6]->force.c, pj[7]->force.c);
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed,
+              pj[4]->force.soundspeed, pj[5]->force.soundspeed, pj[6]->force.soundspeed, pj[7]->force.soundspeed);
   vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
                      pi[3]->force.v_sig, pi[4]->force.v_sig, pi[5]->force.v_sig,
                      pi[6]->force.v_sig, pi[7]->force.v_sig);
@@ -834,18 +830,18 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
                       pj[4]->alpha, pj[5]->alpha, pj[6]->alpha, pj[7]->alpha);
 #elif VEC_SIZE == 4
   mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
-  piPOrho2.v = vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2,
-                       pi[2]->force.POrho2, pi[3]->force.POrho2);
-  pjPOrho2.v = vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2,
-                       pj[2]->force.POrho2, pj[3]->force.POrho2);
+  piPOrho2.v = vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2,
+                       pi[2]->force.P_over_rho2, pi[3]->force.P_over_rho2);
+  pjPOrho2.v = vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2,
+                       pj[2]->force.P_over_rho2, pj[3]->force.P_over_rho2);
   pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho);
   pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho);
   piu.v = vec_set(pi[0]->u, pi[1]->u, pi[2]->u, pi[3]->u);
   pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u);
   ci.v =
-      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c);
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed);
   cj.v =
-      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c);
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed);
   vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
                      pi[3]->force.v_sig);
   vj_sig.v = vec_set(pj[0]->force.v_sig, pj[1]->force.v_sig, pj[2]->force.v_sig,
@@ -936,15 +932,11 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
   /* Add the thermal conductivity */
   piu_dt.v += mj.v * tc.v * (piu.v - pju.v);
 
-  /* compute the signal velocity (this is always symmetrical). */
-  vi_sig.v = vec_fmax(vi_sig.v, v_sig.v);
-  vj_sig.v = vec_fmax(vj_sig.v, v_sig.v);
-
   /* Store the forces back on the particles. */
   for (k = 0; k < VEC_SIZE; k++) {
     pi[k]->force.u_dt += piu_dt.f[k];
     pi[k]->force.h_dt -= pih_dt.f[k];
-    pi[k]->force.v_sig = vi_sig.f[k];
+    pi[k]->force.v_sig = fmaxf(pi[k]->force.v_sig,v_sig.f[k]);
     for (j = 0; j < 3; j++) pi[k]->a_hydro[j] -= pia[j].f[k];
   }
 

src/hydro/Default/hydro_part.h

@@ -90,7 +90,7 @@ struct part {
       float balsara;
 
       /* Aggregate quantities. */
-      float POrho2;
+      float P_over_rho2;
 
       /* Change in particle energy over time. */
       float u_dt;
@@ -99,7 +99,7 @@ struct part {
       float v_sig;
 
       /* Sound speed */
-      float c;
+      float soundspeed;
 
       /* Change in smoothing length over time. */
       float h_dt;

src/hydro/Gadget2/hydro_iact.h

@@ -479,9 +479,177 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
 __attribute__((always_inline)) INLINE static void runner_iact_vec_force(
     float *R2, float *Dx, float *Hi, float *Hj, struct part **pi,
     struct part **pj) {
-  error(
-      "A vectorised version of the Gadget2 force interaction function does not "
-      "exist yet!");
+
+#ifdef WITH_VECTORIZATION
+
+  vector r, r2, ri;
+  vector xi, xj;
+  vector hi, hj, hi_inv, hj_inv;
+  vector hi2_inv, hj2_inv;
+  vector wi, wj, wi_dx, wj_dx, wi_dr, wj_dr, dvdr;
+  vector piPOrho, pjPOrho, pirho, pjrho;
+  vector mi, mj;
+  vector f;
+  vector dx[3];
+  vector vi[3], vj[3];
+  vector pia[3], pja[3];
+  vector pih_dt, pjh_dt;
+  vector ci, cj, v_sig;
+  vector omega_ij, mu_ij, fac_mu, balsara;
+  vector rho_ij, visc, visc_term, sph_term, acc, entropy_dt;
+  int j, k;
+
+  fac_mu.v = vec_set1(1.f); /* Will change with cosmological integration */
+
+  /* Load stuff. */
+#if VEC_SIZE == 8
+  mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass,
+                 pi[4]->mass, pi[5]->mass, pi[6]->mass, pi[7]->mass);
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
+                 pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
+  piPOrho.v =
+      vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2, pi[2]->force.P_over_rho2,
+              pi[3]->force.P_over_rho2, pi[4]->force.P_over_rho2, pi[5]->force.P_over_rho2,
+              pi[6]->force.P_over_rho2, pi[7]->force.P_over_rho2);
+  pjPOrho.v =
+      vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2, pj[2]->force.P_over_rho2,
+              pj[3]->force.P_over_rho2, pj[4]->force.P_over_rho2, pj[5]->force.P_over_rho2,
+              pj[6]->force.P_over_rho2, pj[7]->force.P_over_rho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho, pi[4]->rho,
+                    pi[5]->rho, pi[6]->rho, pi[7]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho, pj[4]->rho,
+                    pj[5]->rho, pj[6]->rho, pj[7]->rho);
+  ci.v =
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed,
+              pi[4]->force.soundspeed, pi[5]->force.soundspeed, pi[6]->force.soundspeed, pi[7]->force.soundspeed);
+  cj.v =
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed,
+              pj[4]->force.soundspeed, pj[5]->force.soundspeed, pj[6]->force.soundspeed, pj[7]->force.soundspeed);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k],
+                      pi[4]->v[k], pi[5]->v[k], pi[6]->v[k], pi[7]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k],
+                      pj[4]->v[k], pj[5]->v[k], pj[6]->v[k], pj[7]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k], Dx[12 + k],
+                      Dx[15 + k], Dx[18 + k], Dx[21 + k]);
+  balsara.v =
+      vec_set(pi[0]->force.balsara, pi[1]->force.balsara, pi[2]->force.balsara,
+              pi[3]->force.balsara, pi[4]->force.balsara, pi[5]->force.balsara,
+              pi[6]->force.balsara, pi[7]->force.balsara) +
+      vec_set(pj[0]->force.balsara, pj[1]->force.balsara, pj[2]->force.balsara,
+              pj[3]->force.balsara, pj[4]->force.balsara, pj[5]->force.balsara,
+              pj[6]->force.balsara, pj[7]->force.balsara);
+#elif VEC_SIZE == 4
+  mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass);
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
+  piPOrho.v = vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2,
+                       pi[2]->force.P_over_rho2, pi[3]->force.P_over_rho2);
+  pjPOrho.v = vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2,
+                       pj[2]->force.P_over_rho2, pj[3]->force.P_over_rho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho);
+  ci.v =
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed);
+  cj.v =
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k]);
+  balsara.v = vec_set(pi[0]->force.balsara, pi[1]->force.balsara,
+                      pi[2]->force.balsara, pi[3]->force.balsara) +
+              vec_set(pj[0]->force.balsara, pj[1]->force.balsara,
+                      pj[2]->force.balsara, pj[3]->force.balsara);
+#else
+  error("Unknown vector size.")
+#endif
+
+  /* Get the radius and inverse radius. */
+  r2.v = vec_load(R2);
+  ri.v = vec_rsqrt(r2.v);
+  ri.v = ri.v - vec_set1(0.5f) * ri.v * (r2.v * ri.v * ri.v - vec_set1(1.0f));
+  r.v = r2.v * ri.v;
+
+  /* Get the kernel for hi. */
+  hi.v = vec_load(Hi);
+  hi_inv.v = vec_rcp(hi.v);
+  hi_inv.v = hi_inv.v - hi_inv.v * (hi.v * hi_inv.v - vec_set1(1.0f));
+  hi2_inv.v = hi_inv.v * hi_inv.v;
+  xi.v = r.v * hi_inv.v;
+  kernel_deval_vec(&xi, &wi, &wi_dx);
+  wi_dr.v = hi2_inv.v * hi2_inv.v * wi_dx.v;
+
+  /* Get the kernel for hj. */
+  hj.v = vec_load(Hj);
+  hj_inv.v = vec_rcp(hj.v);
+  hj_inv.v = hj_inv.v - hj_inv.v * (hj.v * hj_inv.v - vec_set1(1.0f));
+  hj2_inv.v = hj_inv.v * hj_inv.v;
+  xj.v = r.v * hj_inv.v;
+  kernel_deval_vec(&xj, &wj, &wj_dx);
+  wj_dr.v = hj2_inv.v * hj2_inv.v * wj_dx.v;
+
+  /* Compute dv dot r. */
+  dvdr.v = ((vi[0].v - vj[0].v) * dx[0].v) + ((vi[1].v - vj[1].v) * dx[1].v) +
+           ((vi[2].v - vj[2].v) * dx[2].v);
+  //dvdr.v = dvdr.v * ri.v;
+
+  /* Compute the relative velocity. (This is 0 if the particles move away from
+   * each other and negative otherwise) */
+  omega_ij.v = vec_fmin(dvdr.v, vec_set1(0.0f));
+  mu_ij.v = fac_mu.v * ri.v * omega_ij.v; /* This is 0 or negative */
+  
+  /* Compute signal velocity */
+  v_sig.v = ci.v + cj.v - vec_set1(3.0f) * mu_ij.v;
+  
+  /* Now construct the full viscosity term */
+  rho_ij.v = vec_set1(0.5f) * (pirho.v + pjrho.v);
+  visc.v = vec_set1(-0.25f) * vec_set1(const_viscosity_alpha) * v_sig.v * mu_ij.v * 
+           balsara.v / rho_ij.v;
+
+  /* Now, convolve with the kernel */
+  visc_term.v = vec_set1(0.5f) * visc.v * (wi_dr.v + wj_dr.v) * ri.v;
+  sph_term.v = (piPOrho.v * wi_dr.v + pjPOrho.v * wj_dr.v) * ri.v;
+
+  /* Eventually get the acceleration */
+  acc.v = visc_term.v + sph_term.v;
+  
+  /* Use the force, Luke! */
+  for (k = 0; k < 3; k++) {
+    f.v = dx[k].v * acc.v;
+    pia[k].v = mj.v * f.v;
+    pja[k].v = mi.v * f.v;
+  }
+
+  /* Get the time derivative for h. */
+  pih_dt.v = mj.v * dvdr.v * ri.v / pjrho.v * wi_dr.v;
+  pjh_dt.v = mi.v * dvdr.v * ri.v / pirho.v * wj_dr.v;
+
+  /* Change in entropy */
+  entropy_dt.v = vec_set1(0.5f) * visc_term.v * dvdr.v;
+  
+  /* Store the forces back on the particles. */
+  for (k = 0; k < VEC_SIZE; k++) {
+    for (j = 0; j < 3; j++) {
+      pi[k]->a_hydro[j] -= pia[j].f[k];
+      pj[k]->a_hydro[j] += pja[j].f[k];
+    }
+    pi[k]->force.h_dt -= pih_dt.f[k];
+    pj[k]->force.h_dt -= pjh_dt.f[k];
+    pi[k]->force.v_sig = fmaxf(pi[k]->force.v_sig, v_sig.f[k]);
+    pj[k]->force.v_sig = fmaxf(pj[k]->force.v_sig, v_sig.f[k]);
+    pi[k]->entropy_dt += entropy_dt.f[k] * mj.f[k];
+    pj[k]->entropy_dt -= entropy_dt.f[k] * mi.f[k];
+  }
+
+#else 
+
+  error("The Gadget2 serial version of runner_iact_nonsym_force was called when the vectorised version should have been used.")
+
+#endif
 }
 
 /**
@@ -575,9 +743,166 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
 __attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
     float *R2, float *Dx, float *Hi, float *Hj, struct part **pi,
     struct part **pj) {
-  error(
-      "A vectorised version of the Gadget2 non-symmetric force interaction "
-      "function does not exist yet!");
+
+  #ifdef WITH_VECTORIZATION
+
+  vector r, r2, ri;
+  vector xi, xj;
+  vector hi, hj, hi_inv, hj_inv;
+  vector hi2_inv, hj2_inv;
+  vector wi, wj, wi_dx, wj_dx, wi_dr, wj_dr, dvdr;
+  vector piPOrho, pjPOrho, pirho, pjrho;
+  vector mj;
+  vector f;
+  vector dx[3];
+  vector vi[3], vj[3];
+  vector pia[3];
+  vector pih_dt;
+  vector ci, cj, v_sig;
+  vector omega_ij, mu_ij, fac_mu, balsara;
+  vector rho_ij, visc, visc_term, sph_term, acc, entropy_dt;
+  int j, k;
+
+  fac_mu.v = vec_set1(1.f); /* Will change with cosmological integration */
+
+  /* Load stuff. */
+#if VEC_SIZE == 8
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
+                 pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
+  piPOrho.v =
+      vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2, pi[2]->force.P_over_rho2,
+              pi[3]->force.P_over_rho2, pi[4]->force.P_over_rho2, pi[5]->force.P_over_rho2,
+              pi[6]->force.P_over_rho2, pi[7]->force.P_over_rho2);
+  pjPOrho.v =
+      vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2, pj[2]->force.P_over_rho2,
+              pj[3]->force.P_over_rho2, pj[4]->force.P_over_rho2, pj[5]->force.P_over_rho2,
+              pj[6]->force.P_over_rho2, pj[7]->force.P_over_rho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho, pi[4]->rho,
+                    pi[5]->rho, pi[6]->rho, pi[7]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho, pj[4]->rho,
+                    pj[5]->rho, pj[6]->rho, pj[7]->rho);
+  ci.v =
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed,
+              pi[4]->force.soundspeed, pi[5]->force.soundspeed, pi[6]->force.soundspeed, pi[7]->force.soundspeed);
+  cj.v =
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed,
+              pj[4]->force.soundspeed, pj[5]->force.soundspeed, pj[6]->force.soundspeed, pj[7]->force.soundspeed);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k],
+                      pi[4]->v[k], pi[5]->v[k], pi[6]->v[k], pi[7]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k],
+                      pj[4]->v[k], pj[5]->v[k], pj[6]->v[k], pj[7]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k], Dx[12 + k],
+                      Dx[15 + k], Dx[18 + k], Dx[21 + k]);
+  balsara.v =
+      vec_set(pi[0]->force.balsara, pi[1]->force.balsara, pi[2]->force.balsara,
+              pi[3]->force.balsara, pi[4]->force.balsara, pi[5]->force.balsara,
+              pi[6]->force.balsara, pi[7]->force.balsara) +
+      vec_set(pj[0]->force.balsara, pj[1]->force.balsara, pj[2]->force.balsara,
+              pj[3]->force.balsara, pj[4]->force.balsara, pj[5]->force.balsara,
+              pj[6]->force.balsara, pj[7]->force.balsara);
+#elif VEC_SIZE == 4
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
+  piPOrho.v = vec_set(pi[0]->force.P_over_rho2, pi[1]->force.P_over_rho2,
+                       pi[2]->force.P_over_rho2, pi[3]->force.P_over_rho2);
+  pjPOrho.v = vec_set(pj[0]->force.P_over_rho2, pj[1]->force.P_over_rho2,
+                       pj[2]->force.P_over_rho2, pj[3]->force.P_over_rho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho);
+  ci.v =
+      vec_set(pi[0]->force.soundspeed, pi[1]->force.soundspeed, pi[2]->force.soundspeed, pi[3]->force.soundspeed);
+  cj.v =
+      vec_set(pj[0]->force.soundspeed, pj[1]->force.soundspeed, pj[2]->force.soundspeed, pj[3]->force.soundspeed);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(