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authorSteven Rostedt <srostedt@redhat.com>2009-04-29 00:26:30 -0400
committerSteven Rostedt <rostedt@goodmis.org>2009-04-29 00:26:30 -0400
commitf2957f1f196b0217644a17c1379855a118a37d72 (patch)
treef033fac7d01e029f1b3fb5c39f37a80a5e861c4d
parent93459c6cb9816c52200993d29dd18cea1daee335 (diff)
downloadlinux-f2957f1f196b0217644a17c1379855a118a37d72.tar.gz
tracing: have splice only copy full pages
Splice works with pages, it is much more effecient to use an entire page than to copy bits over several pages. Using logdev to trace the internals of the splice mechanism, I was able to see that splice can be very aggressive. When tracing is occurring, and the reader caught up to the writer, and the writer is on the reader page, the reader will copy what is there into the splice page. Splice may iterate over several pages and if the writer is still writing to the page, the reader will keep copying bits to new pages to pass to userspace. This patch changes it to only pass data to userspace if the page is full (the writer has left the page). This has a small side effect that splice can not read a partial page, and must wait for the page to fill. This should not be an issue. If tracing has stopped, then a use of "read" will still read all of the page. [ Impact: better performance for ring buffer splice code ] Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
-rw-r--r--kernel/trace/trace.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0aeb3b93414e..f5427e0fc982 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3542,7 +3542,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
}
r = ring_buffer_read_page(ref->buffer, &ref->page,
- len, info->cpu, 0);
+ len, info->cpu, 1);
if (r < 0) {
ring_buffer_free_read_page(ref->buffer,
ref->page);