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authorSteven Rostedt <srostedt@redhat.com>2009-04-29 00:23:13 -0400
committerSteven Rostedt <rostedt@goodmis.org>2009-04-29 00:23:13 -0400
commit93459c6cb9816c52200993d29dd18cea1daee335 (patch)
tree9ee6a4e9fda5d77d0d05b7855cd2de59fb62d8a0 /kernel
parent5beae6efd1004b44c3e257dc96087978e4c763c1 (diff)
tracing: only add splice page if entries exist
The splice code allocates a page even when the ring buffer is empty. It detects the ring buffer being empty when it it fails to copy anything from the ring buffer into the page. This patch adds a check to see if there is anything in the ring buffer before allocating a page. Thanks to logdev for letting me trace the tracer to find this. [ Impact: speed up due to removing unnecessary allocation ] Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/trace.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9058240c85c..0aeb3b93414 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3508,7 +3508,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
.spd_release = buffer_spd_release,
};
struct buffer_ref *ref;
- int size, i;
+ int entries, size, i;
size_t ret;
if (*ppos & (PAGE_SIZE - 1)) {
@@ -3523,7 +3523,9 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
len &= PAGE_MASK;
}
- for (i = 0; i < PIPE_BUFFERS && len; i++, len -= PAGE_SIZE) {
+ entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
+
+ for (i = 0; i < PIPE_BUFFERS && len && entries; i++, len -= PAGE_SIZE) {
struct page *page;
int r;
@@ -3564,6 +3566,8 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
spd.partial[i].private = (unsigned long)ref;
spd.nr_pages++;
*ppos += PAGE_SIZE;
+
+ entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
}
spd.nr_pages = i;