Arnd Bergmann wrote:

On Monday 29 January 2007 20:48, Maynard Johnson wrote:

quoted

Subject: Enable SPU switch notification to detect currently active SPU tasks.

From: Maynard Johnson <redacted>

This patch adds to the capability of spu_switch_event_register so that the
caller is also notified of currently active SPU tasks.  It also exports
spu_switch_event_register and spu_switch_event_unregister.

Signed-off-by: Maynard Johnson <redacted>

I looked through it again, and think I found a serious bug, but that
should be easy enough to solve:

quoted

+static void notify_spus_active(void)
+{
+       int node;
+       /* Wake up the active spu_contexts. When the awakened processes 
+        * sees their notify_active flag is set, they will call
+        * spu_switch_notify();
+        */
+       for (node = 0; node < MAX_NUMNODES; node++) {
+               struct spu *spu;
+               mutex_lock(&spu_prio->active_mutex[node]);
+                list_for_each_entry(spu, &spu_prio->active_list[node], list) {
+                       struct spu_context *ctx = spu->ctx;

[side note]
There is a small whitespace breakage in here, please make sure you always
use tabs for indenting, not space characters.
[/side note]

quoted

@@ -45,9 +45,10 @@
       u64 pte_fault;

       *stat = ctx->ops->status_read(ctx);
-       if (ctx->state != SPU_STATE_RUNNABLE)
-               return 1;
+
       spu = ctx->spu;
+       if (ctx->state != SPU_STATE_RUNNABLE || spu->notify_active)
+               return 1;
       pte_fault = spu->dsisr &
           (MFC_DSISR_PTE_NOT_FOUND | MFC_DSISR_ACCESS_DENIED);
       return (!(*stat & 0x1) || pte_fault || spu->class_0_pending) ? 1 : 0;

@@ -305,6 +306,7 @@
                  u32 *npc, u32 *event)

{
       int ret;
+       struct spu * spu;
       u32 status;

       if (down_interruptible(&ctx->run_sema))

@@ -318,8 +320,16 @@

       do {
               ret = spufs_wait(ctx->stop_wq, spu_stopped(ctx, &status));
+               spu = ctx->spu;
               if (unlikely(ret))
                       break;
+               if (unlikely(spu->notify_active)) {
+                       spu->notify_active = 0;
+                       if (!(status & SPU_STATUS_STOPPED_BY_STOP)) {
+                               spu_switch_notify(spu, ctx);
+                               continue;
+                       }
+               }

This is before spu_reacquire_runnable, so in case the spu got
preempted at the same time when oprofile was enabled, ctx->spu
is NULL, and you can't load the notify_active flag from it.

On solution would be to move the notify_active flag from ctx->spu
into ctx itself, but maybe there are other ways to solve this.

In an earlier review of this patch, Christopher Hellwig suggested I move 
the notify_active flag to be a bit in the sched_flags field that's added 
in his scheduler patch series.  If this patch series will be a available 
in an "Arnd" tree that we'll be using for our current OProfile 
development, perhaps I should wait until that time to change this, since 
the window of vulnerability is quite small.  What do you think?

-Maynard

Thanks,

	Arnd <><