[POWERPC] spufs: add context switch notification log

There are userspace instrumentation tools that need to monitor spu
context switches. This patch adds a new file called 'switch_log' to
each spufs context directory that can be used to monitor the context
switches.

Context switch in/out and exit from spu_run are monitored after the
file was first opened and can be read from it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

5 files changed, 200 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/cell/spufs/context.c b/arch/powerpc/platforms/cell/spufs/context.c
index 0ad83aeb70b1..91f2d4d9aefd 100644
--- a/arch/powerpc/platforms/cell/spufs/context.c
+++ b/arch/powerpc/platforms/cell/spufs/context.c
@@ -88,6 +88,7 @@ void destroy_spu_context(struct kref *kref)
                 kref_put(ctx->prof_priv_kref, ctx->prof_priv_release);
         BUG_ON(!list_empty(&ctx->rq));
         atomic_dec(&nr_spu_contexts);
+        kfree(ctx->switch_log);
         kfree(ctx);
 }
 
diff --git a/arch/powerpc/platforms/cell/spufs/file.c b/arch/powerpc/platforms/cell/spufs/file.c
index ba791e931bd6..b5c1505cf58b 100644
--- a/arch/powerpc/platforms/cell/spufs/file.c
+++ b/arch/powerpc/platforms/cell/spufs/file.c
@@ -2387,6 +2387,171 @@ static const struct file_operations spufs_stat_fops = {
         .release        = single_release,
 };
 
+static inline int spufs_switch_log_used(struct spu_context *ctx)
+{
+        return (ctx->switch_log->head - ctx->switch_log->tail) %
+                SWITCH_LOG_BUFSIZE;
+}
+
+static inline int spufs_switch_log_avail(struct spu_context *ctx)
+{
+        return SWITCH_LOG_BUFSIZE - spufs_switch_log_used(ctx);
+}
+
+static int spufs_switch_log_open(struct inode *inode, struct file *file)
+{
+        struct spu_context *ctx = SPUFS_I(inode)->i_ctx;
+
+        /*
+         * We (ab-)use the mapping_lock here because it serves the similar
+         * purpose for synchronizing open/close elsewhere.  Maybe it should
+         * be renamed eventually.
+         */
+        mutex_lock(&ctx->mapping_lock);
+        if (ctx->switch_log) {
+                spin_lock(&ctx->switch_log->lock);
+                ctx->switch_log->head = 0;
+                ctx->switch_log->tail = 0;
+                spin_unlock(&ctx->switch_log->lock);
+        } else {
+                /*
+                 * We allocate the switch log data structures on first open.
+                 * They will never be free because we assume a context will
+                 * be traced until it goes away.
+                 */
+                ctx->switch_log = kzalloc(sizeof(struct switch_log) +
+                        SWITCH_LOG_BUFSIZE * sizeof(struct switch_log_entry),
+                        GFP_KERNEL);
+                if (!ctx->switch_log)
+                        goto out;
+                spin_lock_init(&ctx->switch_log->lock);
+                init_waitqueue_head(&ctx->switch_log->wait);
+        }
+        mutex_unlock(&ctx->mapping_lock);
+
+        return 0;
+ out:
+        mutex_unlock(&ctx->mapping_lock);
+        return -ENOMEM;
+}
+
+static int switch_log_sprint(struct spu_context *ctx, char *tbuf, int n)
+{
+        struct switch_log_entry *p;
+
+        p = ctx->switch_log->log + ctx->switch_log->tail % SWITCH_LOG_BUFSIZE;
+
+        return snprintf(tbuf, n, "%u.%09u %d %u %u %llu\n",
+                        (unsigned int) p->tstamp.tv_sec,
+                        (unsigned int) p->tstamp.tv_nsec,
+                        p->spu_id,
+                        (unsigned int) p->type,
+                        (unsigned int) p->val,
+                        (unsigned long long) p->timebase);
+}
+
+static ssize_t spufs_switch_log_read(struct file *file, char __user *buf,
+                             size_t len, loff_t *ppos)
+{
+        struct inode *inode = file->f_path.dentry->d_inode;
+        struct spu_context *ctx = SPUFS_I(inode)->i_ctx;
+        int error = 0, cnt = 0;
+
+        if (!buf || len < 0)
+                return -EINVAL;
+
+        while (cnt < len) {
+                char tbuf[128];
+                int width;
+
+                if (file->f_flags & O_NONBLOCK) {
+                        if (spufs_switch_log_used(ctx) <= 0)
+                                return cnt ? cnt : -EAGAIN;
+                } else {
+                        /* Wait for data in buffer */
+                        error = wait_event_interruptible(ctx->switch_log->wait,
+                                        spufs_switch_log_used(ctx) > 0);
+                        if (error)
+                                break;
+                }
+
+                spin_lock(&ctx->switch_log->lock);
+                if (ctx->switch_log->head == ctx->switch_log->tail) {
+                        /* multiple readers race? */
+                        spin_unlock(&ctx->switch_log->lock);
+                        continue;
+                }
+
+                width = switch_log_sprint(ctx, tbuf, sizeof(tbuf));
+                if (width < len) {
+                        ctx->switch_log->tail =
+                                (ctx->switch_log->tail + 1) %
+                                 SWITCH_LOG_BUFSIZE;
+                }
+
+                spin_unlock(&ctx->switch_log->lock);
+
+                /*
+                 * If the record is greater than space available return
+                 * partial buffer (so far)
+                 */
+                if (width >= len)
+                        break;
+
+                error = copy_to_user(buf + cnt, tbuf, width);
+                if (error)
+                        break;
+                cnt += width;
+        }
+
+        return cnt == 0 ? error : cnt;
+}
+
+static unsigned int spufs_switch_log_poll(struct file *file, poll_table *wait)
+{
+        struct inode *inode = file->f_path.dentry->d_inode;
+        struct spu_context *ctx = SPUFS_I(inode)->i_ctx;
+        unsigned int mask = 0;
+
+        poll_wait(file, &ctx->switch_log->wait, wait);
+
+        if (spufs_switch_log_used(ctx) > 0)
+                mask |= POLLIN;
+
+        return mask;
+}
+
+static const struct file_operations spufs_switch_log_fops = {
+        .owner  = THIS_MODULE,
+        .open   = spufs_switch_log_open,
+        .read   = spufs_switch_log_read,
+        .poll   = spufs_switch_log_poll,
+};
+
+void spu_switch_log_notify(struct spu *spu, struct spu_context *ctx,
+                u32 type, u32 val)
+{
+        if (!ctx->switch_log)
+                return;
+
+        spin_lock(&ctx->switch_log->lock);
+        if (spufs_switch_log_avail(ctx) > 1) {
+                struct switch_log_entry *p;
+
+                p = ctx->switch_log->log + ctx->switch_log->head;
+                ktime_get_ts(&p->tstamp);
+                p->timebase = get_tb();
+                p->spu_id = spu ? spu->number : -1;
+                p->type = type;
+                p->val = val;
+
+                ctx->switch_log->head =
+                        (ctx->switch_log->head + 1) % SWITCH_LOG_BUFSIZE;
+        }
+        spin_unlock(&ctx->switch_log->lock);
+
+        wake_up(&ctx->switch_log->wait);
+}
 
 struct tree_descr spufs_dir_contents[] = {
         { "capabilities", &spufs_caps_fops, 0444, },
@@ -2423,6 +2588,7 @@ struct tree_descr spufs_dir_contents[] = {
         { "proxydma_info", &spufs_proxydma_info_fops, 0444, },
         { "tid", &spufs_tid_fops, 0444, },
         { "stat", &spufs_stat_fops, 0444, },
+        { "switch_log", &spufs_switch_log_fops, 0444 },
         {},
 };
 
diff --git a/arch/powerpc/platforms/cell/spufs/run.c b/arch/powerpc/platforms/cell/spufs/run.c
index 96bf7c2b86fc..a9c35b7b719f 100644
--- a/arch/powerpc/platforms/cell/spufs/run.c
+++ b/arch/powerpc/platforms/cell/spufs/run.c
@@ -405,6 +405,8 @@ long spufs_run_spu(struct spu_context *ctx, u32 *npc, u32 *event)
         ret = spu_run_fini(ctx, npc, &status);
         spu_yield(ctx);
 
+        spu_switch_log_notify(NULL, ctx, SWITCH_LOG_EXIT, status);
+
         if ((status & SPU_STATUS_STOPPED_BY_STOP) &&
             (((status >> SPU_STOP_STATUS_SHIFT) & 0x3f00) == 0x2100))
                 ctx->stats.libassist++;
diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 00528ef84ad2..31e9d85761c2 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -240,6 +240,7 @@ static void spu_bind_context(struct spu *spu, struct spu_context *ctx)
         spu->mfc_callback = spufs_mfc_callback;
         mb();
         spu_unmap_mappings(ctx);
+        spu_switch_log_notify(spu, ctx, SWITCH_LOG_START, 0);
         spu_restore(&ctx->csa, spu);
         spu->timestamp = jiffies;
         spu_cpu_affinity_set(spu, raw_smp_processor_id());
@@ -419,6 +420,7 @@ static void spu_unbind_context(struct spu *spu, struct spu_context *ctx)
         spu_switch_notify(spu, NULL);
         spu_unmap_mappings(ctx);
         spu_save(&ctx->csa, spu);
+        spu_switch_log_notify(spu, ctx, SWITCH_LOG_STOP, 0);
         spu->timestamp = jiffies;
         ctx->state = SPU_STATE_SAVED;
         spu->ibox_callback = NULL;
diff --git a/arch/powerpc/platforms/cell/spufs/spufs.h b/arch/powerpc/platforms/cell/spufs/spufs.h
index cdc515182f82..dd63b16bb072 100644
--- a/arch/powerpc/platforms/cell/spufs/spufs.h
+++ b/arch/powerpc/platforms/cell/spufs/spufs.h
@@ -47,6 +47,30 @@ enum {
         SPU_SCHED_SPU_RUN,      /* context is within spu_run */
 };
 
+enum {
+        SWITCH_LOG_BUFSIZE = 4096,
+};
+
+enum {
+        SWITCH_LOG_START,
+        SWITCH_LOG_STOP,
+        SWITCH_LOG_EXIT,
+};
+
+struct switch_log {
+        spinlock_t              lock;
+        wait_queue_head_t       wait;
+        unsigned long           head;
+        unsigned long           tail;
+        struct switch_log_entry {
+                struct timespec tstamp;
+                s32             spu_id;
+                u32             type;
+                u32             val;
+                u64             timebase;
+        } log[];
+};
+
 struct spu_context {
         struct spu *spu;                  /* pointer to a physical SPU */
         struct spu_state csa;             /* SPU context save area. */
@@ -116,6 +140,9 @@ struct spu_context {
                 unsigned long long libassist;
         } stats;
 
+        /* context switch log */
+        struct switch_log *switch_log;
+
         struct list_head aff_list;
         int aff_head;
         int aff_offset;
@@ -256,6 +283,8 @@ int spu_activate(struct spu_context *ctx, unsigned long flags);
 void spu_deactivate(struct spu_context *ctx);
 void spu_yield(struct spu_context *ctx);
 void spu_switch_notify(struct spu *spu, struct spu_context *ctx);
+void spu_switch_log_notify(struct spu *spu, struct spu_context *ctx,
+                u32 type, u32 val);
 void spu_set_timeslice(struct spu_context *ctx);
 void spu_update_sched_info(struct spu_context *ctx);
 void __spu_update_sched_info(struct spu_context *ctx);