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authorAlexander Shishkin <alexander.shishkin@linux.intel.com>2017-09-06 19:08:11 +0300
committerIngo Molnar <mingo@kernel.org>2017-09-29 10:06:45 +0200
commit441430eb54a00586f95f1aefc48e0801bbd6a923 (patch)
tree9e9bfffb3625e73466e63120ad9014980c97be46
parent770b782f555d663d133fcd4dc1632023f79357b9 (diff)
downloadlinux-stericsson-441430eb54a00586f95f1aefc48e0801bbd6a923.tar.gz
perf/aux: Only update ->aux_wakeup in non-overwrite mode
The following commit: d9a50b0256 ("perf/aux: Ensure aux_wakeup represents most recent wakeup index") changed the AUX wakeup position calculation to rounddown(), which causes a division-by-zero in AUX overwrite mode (aka "snapshot mode"). The zero denominator results from the fact that perf record doesn't set aux_watermark to anything, in which case the kernel will set it to half the AUX buffer size, but only for non-overwrite mode. In the overwrite mode aux_watermark stays zero. The good news is that, AUX overwrite mode, wakeups don't happen and related bookkeeping is not relevant, so we can simply forego the whole wakeup updates. Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/20170906160811.16510-1-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/events/ring_buffer.c20
1 files changed, 15 insertions, 5 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index af71a84e12ee..f684d8e5fa2b 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -412,6 +412,19 @@ err:
return NULL;
}
+static bool __always_inline rb_need_aux_wakeup(struct ring_buffer *rb)
+{
+ if (rb->aux_overwrite)
+ return false;
+
+ if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) {
+ rb->aux_wakeup = rounddown(rb->aux_head, rb->aux_watermark);
+ return true;
+ }
+
+ return false;
+}
+
/*
* Commit the data written by hardware into the ring buffer by adjusting
* aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the
@@ -451,10 +464,8 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
}
rb->user_page->aux_head = rb->aux_head;
- if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) {
+ if (rb_need_aux_wakeup(rb))
wakeup = true;
- rb->aux_wakeup = rounddown(rb->aux_head, rb->aux_watermark);
- }
if (wakeup) {
if (handle->aux_flags & PERF_AUX_FLAG_TRUNCATED)
@@ -484,9 +495,8 @@ int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)
rb->aux_head += size;
rb->user_page->aux_head = rb->aux_head;
- if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) {
+ if (rb_need_aux_wakeup(rb)) {
perf_output_wakeup(handle);
- rb->aux_wakeup = rounddown(rb->aux_head, rb->aux_watermark);
handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
}