[CELL] cell: add placement computation for scheduling of affinity contexts

This patch provides the spu affinity placement logic for the spufs scheduler.
Each time a gang is going to be scheduled, the placement of a reference
context is defined. The placement of all other contexts with affinity from
the gang is defined based on this reference context location and on a
precomputed displacement offset.

Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

3 files changed, 151 insertions, 1 deletions

diff --git a/arch/powerpc/platforms/cell/spufs/gang.c b/arch/powerpc/platforms/cell/spufs/gang.c
index 0a752ce67c8a..71a443253021 100644
--- a/arch/powerpc/platforms/cell/spufs/gang.c
+++ b/arch/powerpc/platforms/cell/spufs/gang.c
@@ -75,8 +75,10 @@ void spu_gang_remove_ctx(struct spu_gang *gang, struct spu_context *ctx)
 {
         mutex_lock(&gang->mutex);
         WARN_ON(ctx->gang != gang);
-        if (!list_empty(&ctx->aff_list))
+        if (!list_empty(&ctx->aff_list)) {
                 list_del_init(&ctx->aff_list);
+                gang->aff_flags &= ~AFF_OFFSETS_SET;
+        }
         list_del_init(&ctx->gang_list);
         gang->contexts--;
         mutex_unlock(&gang->mutex);
diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 6d0ab72cc70e..a9569de4c141 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -233,6 +233,8 @@ static void spu_bind_context(struct spu *spu, struct spu_context *ctx)
 
         if (ctx->flags & SPU_CREATE_NOSCHED)
                 atomic_inc(&cbe_spu_info[spu->node].reserved_spus);
+        if (!list_empty(&ctx->aff_list))
+                atomic_inc(&ctx->gang->aff_sched_count);
 
         ctx->stats.slb_flt_base = spu->stats.slb_flt;
         ctx->stats.class2_intr_base = spu->stats.class2_intr;
@@ -259,6 +261,143 @@ static void spu_bind_context(struct spu *spu, struct spu_context *ctx)
         spuctx_switch_state(ctx, SPU_UTIL_IDLE_LOADED);
 }
 
+/*
+ * XXX(hch): needs locking.
+ */
+static inline int sched_spu(struct spu *spu)
+{
+        return (!spu->ctx || !(spu->ctx->flags & SPU_CREATE_NOSCHED));
+}
+
+static void aff_merge_remaining_ctxs(struct spu_gang *gang)
+{
+        struct spu_context *ctx;
+
+        list_for_each_entry(ctx, &gang->aff_list_head, aff_list) {
+                if (list_empty(&ctx->aff_list))
+                        list_add(&ctx->aff_list, &gang->aff_list_head);
+        }
+        gang->aff_flags |= AFF_MERGED;
+}
+
+static void aff_set_offsets(struct spu_gang *gang)
+{
+        struct spu_context *ctx;
+        int offset;
+
+        offset = -1;
+        list_for_each_entry_reverse(ctx, &gang->aff_ref_ctx->aff_list,
+                                                                aff_list) {
+                if (&ctx->aff_list == &gang->aff_list_head)
+                        break;
+                ctx->aff_offset = offset--;
+        }
+
+        offset = 0;
+        list_for_each_entry(ctx, gang->aff_ref_ctx->aff_list.prev, aff_list) {
+                if (&ctx->aff_list == &gang->aff_list_head)
+                        break;
+                ctx->aff_offset = offset++;
+        }
+
+        gang->aff_flags |= AFF_OFFSETS_SET;
+}
+
+static struct spu *aff_ref_location(struct spu_context *ctx, int mem_aff,
+                 int group_size, int lowest_offset)
+{
+        struct spu *spu;
+        int node, n;
+
+        /*
+         * TODO: A better algorithm could be used to find a good spu to be
+         *       used as reference location for the ctxs chain.
+         */
+        node = cpu_to_node(raw_smp_processor_id());
+        for (n = 0; n < MAX_NUMNODES; n++, node++) {
+                node = (node < MAX_NUMNODES) ? node : 0;
+                if (!node_allowed(ctx, node))
+                        continue;
+                list_for_each_entry(spu, &cbe_spu_info[node].spus, cbe_list) {
+                        if ((!mem_aff || spu->has_mem_affinity) &&
+                                                        sched_spu(spu))
+                                return spu;
+                }
+        }
+        return NULL;
+}
+
+static void aff_set_ref_point_location(struct spu_gang *gang)
+{
+        int mem_aff, gs, lowest_offset;
+        struct spu_context *ctx;
+        struct spu *tmp;
+
+        mem_aff = gang->aff_ref_ctx->flags & SPU_CREATE_AFFINITY_MEM;
+        lowest_offset = 0;
+        gs = 0;
+
+        list_for_each_entry(tmp, &gang->aff_list_head, aff_list)
+                gs++;
+
+        list_for_each_entry_reverse(ctx, &gang->aff_ref_ctx->aff_list,
+                                                                aff_list) {
+                if (&ctx->aff_list == &gang->aff_list_head)
+                        break;
+                lowest_offset = ctx->aff_offset;
+        }
+
+        gang->aff_ref_spu = aff_ref_location(ctx, mem_aff, gs, lowest_offset);
+}
+
+static struct spu *ctx_location(struct spu *ref, int offset)
+{
+        struct spu *spu;
+
+        spu = NULL;
+        if (offset >= 0) {
+                list_for_each_entry(spu, ref->aff_list.prev, aff_list) {
+                        if (offset == 0)
+                                break;
+                        if (sched_spu(spu))
+                                offset--;
+                }
+        } else {
+                list_for_each_entry_reverse(spu, ref->aff_list.next, aff_list) {
+                        if (offset == 0)
+                                break;
+                        if (sched_spu(spu))
+                                offset++;
+                }
+        }
+        return spu;
+}
+
+/*
+ * affinity_check is called each time a context is going to be scheduled.
+ * It returns the spu ptr on which the context must run.
+ */
+struct spu *affinity_check(struct spu_context *ctx)
+{
+        struct spu_gang *gang;
+
+        if (list_empty(&ctx->aff_list))
+                return NULL;
+        gang = ctx->gang;
+        mutex_lock(&gang->aff_mutex);
+        if (!gang->aff_ref_spu) {
+                if (!(gang->aff_flags & AFF_MERGED))
+                        aff_merge_remaining_ctxs(gang);
+                if (!(gang->aff_flags & AFF_OFFSETS_SET))
+                        aff_set_offsets(gang);
+                aff_set_ref_point_location(gang);
+        }
+        mutex_unlock(&gang->aff_mutex);
+        if (!gang->aff_ref_spu)
+                return NULL;
+        return ctx_location(gang->aff_ref_spu, ctx->aff_offset);
+}
+
 /**
  * spu_unbind_context - unbind spu context from physical spu
  * @spu:        physical spu to unbind from
@@ -272,6 +411,9 @@ static void spu_unbind_context(struct spu *spu, struct spu_context *ctx)
 
         if (spu->ctx->flags & SPU_CREATE_NOSCHED)
                 atomic_dec(&cbe_spu_info[spu->node].reserved_spus);
+        if (!list_empty(&ctx->aff_list))
+                if (atomic_dec_and_test(&ctx->gang->aff_sched_count))
+                        ctx->gang->aff_ref_spu = NULL;
         spu_switch_notify(spu, NULL);
         spu_unmap_mappings(ctx);
         spu_save(&ctx->csa, spu);
diff --git a/arch/powerpc/platforms/cell/spufs/spufs.h b/arch/powerpc/platforms/cell/spufs/spufs.h
index 36da17987e9c..42d8da8f0fb5 100644
--- a/arch/powerpc/platforms/cell/spufs/spufs.h
+++ b/arch/powerpc/platforms/cell/spufs/spufs.h
@@ -112,6 +112,7 @@ struct spu_context {
 
         struct list_head aff_list;
         int aff_head;
+        int aff_offset;
 };
 
 struct spu_gang {
@@ -124,6 +125,8 @@ struct spu_gang {
         struct list_head aff_list_head;
         struct mutex aff_mutex;
         int aff_flags;
+        struct spu *aff_ref_spu;
+        atomic_t aff_sched_count;
 };
 
 /* Flag bits for spu_gang aff_flags */
@@ -208,6 +211,9 @@ void spu_gang_add_ctx(struct spu_gang *gang, struct spu_context *ctx);
 /* fault handling */
 int spufs_handle_class1(struct spu_context *ctx);
 
+/* affinity */
+struct spu *affinity_check(struct spu_context *ctx);
+
 /* context management */
 extern atomic_t nr_spu_contexts;
 static inline void spu_acquire(struct spu_context *ctx)