Patch "perf/x86/intel/pt: Generate PMI in the STOP region as well" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

perf/x86/intel/pt: Generate PMI in the STOP region as well

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-x86-intel-pt-generate-pmi-in-the-stop-region-as-well.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexander Shishkin <[email protected]>
Date: Tue, 10 May 2016 16:18:32 +0300
Subject: perf/x86/intel/pt: Generate PMI in the STOP region as well

From: Alexander Shishkin <[email protected]>

commit ab92b232ae05c382c3df0e3d6a5c6d16b639ac8c upstream.

Currently, the PT driver always sets the PMI bit one region (page) before the STOP region so that we can wake up the consumer before we run out of room in the buffer and have to disable the event. However, we also need an interrupt in the last output region, so that we actually get to disable the event (if no more room from new data is available at that point), otherwise hardware just quietly refuses to start, but the event is scheduled in and we end up losing trace data till the event gets removed.

For a cpu-wide event it is even worse since there may not be any re-scheduling at all and no chance for the ring buffer code to notice that its buffer is filled up and the event needs to be disabled (so that the consumer can re-enable it when it finishes reading the data out). In other words, all the trace data will be lost after the buffer gets filled up.

This patch makes PT also generate a PMI when the last output region is full.

@@ -709,6 +709,7 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 
 	/* clear STOP and INT from current entry */
 	buf->topa_index[buf->stop_pos]->stop = 0;
+	buf->topa_index[buf->stop_pos]->intr = 0;
 	buf->topa_index[buf->intr_pos]->intr = 0;
 
 	/* how many pages till the STOP marker */

@@ -733,6 +734,7 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 	buf->intr_pos = idx;
 
 	buf->topa_index[buf->stop_pos]->stop = 1;
+	buf->topa_index[buf->stop_pos]->intr = 1;
 	buf->topa_index[buf->intr_pos]->intr = 1;
 
 	return 0;

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/perf-x86-intel-pt-generate-pmi-in-the-stop-region-as-well.patch queue-4.5/perf-core-fix-perf_event_open-vs.-execve-race.patch