Carl Love wrote:
Subject: Add support to OProfile for profiling Cell BE SPUs
From: Maynard Johnson <[EMAIL PROTECTED]>
This patch updates the existing arch/powerpc/oprofile/op_model_cell.c
to add in the SPU profiling capabilities. In addition, a 'cell' subdirectory
was added to arch/powerpc/oprofile to hold Cell-specific SPU profiling
code.
Signed-off-by: Carl Love <[EMAIL PROTECTED]>
Signed-off-by: Maynard Johnson <[EMAIL PROTECTED]>
Index: linux-2.6.20-rc1/arch/powerpc/configs/cell_defconfig
I've discovered more problems with the kref handling for the cached_info
object that we store in the spu_context. :-(
When the OProfile module initially determines that no cached_info yet
exists for a given spu_context, it creates the cached_info, inits the
cached_info's kref (which increments the refcount) and does a kref_get
(for SPUFS' ref) before passing the cached_info reference off to SUPFS
to store into the spu_context. When OProfile shuts down or the SPU job
ends, OProfile gives up its ref to the cached_info with kref_put. Then
when SPUFS destroys the spu_context, it also gives up its ref. HOWEVER
. . . . If OProfile shuts down while the SPU job is still active _and_
_then_ is restarted while the job is still active, OProfile will find
that the cached_info exists for the given spu_context, so it won't go
through the process of creating it and doing kref_init on the kref.
Under this scenario, OProfile does not own a ref of its own to the
cached_info, and should not be doing a kref_put when done using the
cached_info -- but it does, and so does SPUFS when the spu_context is
destroyed. The end result (with the code as currently written) is that
an extra kref_put is done when the refcount is already down to zero. To
fix this, OProfile needs to detect when it finds an existing cached_info
already stored in the spu_context. Then, instead of creating a new one,
it sets a reminder flag to be used later when it's done using the cached
info to indicate whether or not it needs to call kref_put.
Unfortunately, there's another problem (one that should have been
obvious to me). The cached_info's kref "release" function is
destroy_cached_info(), defined in the OProfile module. If the OProfile
module is unloaded when SPUFS destroys the spu_context and calls
kref_put on the cached_info's kref -- KABOOM! The destroy_cached_info
function (the second arg to kref_put) is not in memory, so we get a
paging fault. I see a couple options to solve this:
1) Don't store the cached_info in the spu_context. Basically, go
back to the simplistic model of creating/deleting the cached_info on
every SPU task activation/deactivation.
2) If there's some way to do this, force the OProfile module to
stay loaded until SPUFS has destroyed its last spu_context that holds a
cached_info object.
I thought about putting the cached_info's kref "release" function in
SPUFS, but this just won't work. This implies that SPUFS needs to know
about the structure of the cached_info, e.g., that it contains the
vma_map member that needs to be freed. But even with that information,
it's not enough, since the vma_map member consists of list of vma_maps,
which is why we have the vma_map_free() function. So SPUFS would still
need access to vma_map_free() from the OProfile module.
Opinions from others would be appreciated.
Thanks.
-Maynard
+/* Container for caching information about an active SPU task.
+ *
+ */
+struct cached_info {
+ struct vma_to_fileoffset_map * map;
+ struct spu * the_spu; /* needed to access pointer to local_store */
+ struct kref cache_ref;
+};
+
+static struct cached_info * spu_info[MAX_NUMNODES * 8];
+
+static void destroy_cached_info(struct kref * kref)
+{
+ struct cached_info * info;
+ info = container_of(kref, struct cached_info, cache_ref);
+ vma_map_free(info->map);
+ kfree(info);
+}
+
+/* Return the cached_info for the passed SPU number.
+ *
+ */
+static struct cached_info * get_cached_info(struct spu * the_spu, int spu_num)
+{
+ struct cached_info * ret_info = NULL;
+ unsigned long flags = 0;
+ if (spu_num >= num_spu_nodes) {
+ printk(KERN_ERR "SPU_PROF: "
+ "%s, line %d: Invalid index %d into spu info cache\n",
+ __FUNCTION__, __LINE__, spu_num);
+ goto out;
+ }
+ spin_lock_irqsave(&cache_lock, flags);
+ if (!spu_info[spu_num] && the_spu)
+ spu_info[spu_num] = (struct cached_info *)
+ spu_get_profile_private(the_spu->ctx);
+
+ ret_info = spu_info[spu_num];
+ spin_unlock_irqrestore(&cache_lock, flags);
+ out:
+ return ret_info;
+}
+
+
+/* Looks for cached info for the passed spu. If not found, the
+ * cached info is created for the passed spu.
+ * Returns 0 for success; otherwise, -1 for error.
+ */
+static int
+prepare_cached_spu_info(struct spu * spu, unsigned int objectId)
+{
+ unsigned long flags = 0;
+ struct vma_to_fileoffset_map * new_map;
+ int retval = 0;
+ struct cached_info * info = get_cached_info(spu, spu->number);
+
+ if (info) {
+ pr_debug("Found cached SPU info.\n");
+ goto out;
+ }
+
+ /* Create cached_info and set spu_info[spu->number] to point to it.
+ * spu->number is a system-wide value, not a per-node value.
+ */
+ info = kzalloc(sizeof(struct cached_info), GFP_KERNEL);
+ if (!info) {
+ printk(KERN_ERR "SPU_PROF: "
+ "%s, line %d: create vma_map failed\n",
+ __FUNCTION__, __LINE__);
+ goto err_alloc;
+ }
+ new_map = create_vma_map(spu, objectId);
+ if (!new_map) {
+ printk(KERN_ERR "SPU_PROF: "
+ "%s, line %d: create vma_map failed\n",
+ __FUNCTION__, __LINE__);
+ goto err_alloc;
+ }
+
+ pr_debug("Created vma_map\n");
+ info->map = new_map;
+ info->the_spu = spu;
+ kref_init(&info->cache_ref);
+ spin_lock_irqsave(&cache_lock, flags);
+ spu_info[spu->number] = info;
+ spin_unlock_irqrestore(&cache_lock, flags);
+ /* Increment count before passing off ref to SPUFS. */
+ kref_get(&info->cache_ref);
+ spu_set_profile_private(spu->ctx, info, &info->cache_ref,
+ destroy_cached_info);
+ goto out;
+
+err_alloc:
+ retval = -1;
+out:
+ return retval;
+}
+
+/*
+ * NOTE: The caller is responsible for locking the
+ * cache_lock prior to calling this function.
+ */
+static int release_cached_info(int spu_index)
+{
+ int index, end;
+ if (spu_index == RELEASE_ALL) {
+ end = num_spu_nodes;
+ index = 0;
+ } else {
+ if (spu_index >= num_spu_nodes) {
+ printk(KERN_ERR "SPU_PROF: "
+ "%s, line %d: Invalid index %d into spu info
cache\n",
+ __FUNCTION__, __LINE__, spu_index);
+ goto out;
+ }
+ end = spu_index +1;
+ index = spu_index;
+ }
+ for (; index < end; index++) {
+ if (spu_info[index]) {
+ kref_put(&spu_info[index]->cache_ref,
destroy_cached_info);
+ spu_info[index] = NULL;
+ }
+ }
+
+out:
+ return 0;
+}
+
Index: linux-2.6.20-rc1/arch/powerpc/platforms/cell/spufs/context.c
===================================================================
--- linux-2.6.20-rc1.orig/arch/powerpc/platforms/cell/spufs/context.c
2007-02-05 14:42:04.359859432 -0600
+++ linux-2.6.20-rc1/arch/powerpc/platforms/cell/spufs/context.c
2007-02-06 16:44:05.983965096 -0600
@@ -22,6 +22,7 @@
#include <linux/fs.h>
#include <linux/mm.h>
+#include <linux/module.h>
#include <linux/slab.h>
#include <asm/spu.h>
#include <asm/spu_csa.h>
@@ -71,6 +72,8 @@
spu_fini_csa(&ctx->csa);
if (ctx->gang)
spu_gang_remove_ctx(ctx->gang, ctx);
+ if (ctx->prof_priv_kref)
+ kref_put(ctx->prof_priv_kref, ctx->prof_priv_release);
kfree(ctx);
}
@@ -200,3 +203,29 @@
downgrade_write(&ctx->state_sema);
}
+
+/* This interface allows a profiler (e.g., OProfile) to store
+ * spu_context information needed for profiling, allowing it to
+ * be saved across context save/restore operation.
+ *
+ * Assumes the caller has already incremented the ref count to
+ * profile_info; then spu_context_destroy must call kref_put
+ * on prof_info_kref.
+ */
+void spu_set_profile_private(struct spu_context * ctx, void * profile_info,
+ struct kref * prof_info_kref,
+ void (* prof_info_release) (struct kref * kref))
+{
+ ctx->profile_private = profile_info;
+ ctx->prof_priv_kref = prof_info_kref;
+ ctx->prof_priv_release = prof_info_release;
+}
+EXPORT_SYMBOL_GPL(spu_set_profile_private);
+
+void * spu_get_profile_private(struct spu_context * ctx)
+{
+ return ctx->profile_private;
+}
+EXPORT_SYMBOL_GPL(spu_get_profile_private);
+
+
-
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