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>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9058240..0aeb3b9 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3508,7 +3508,7 @@
.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 @@
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 @@
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;