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perf: Add a capability for AUX_NO_SG pmus to do software double buffering

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For pmus that don't support scatter-gather for AUX data in hardware, it
might still make sense to implement software double buffering to avoid
losing data while the user is reading data out. For this purpose, add
a pmu capability that guarantees multiple high-order chunks for AUX buffer,
so that the pmu driver can do switchover tricks.

To make use of this feature, add PERF_PMU_CAP_AUX_SW_DOUBLEBUF to your
pmu's capability mask. This will make the ring buffer AUX allocation code
ensure that the biggest high order allocation for the aux buffer pages is
no bigger than half of the total requested buffer size, thus making sure
that the buffer has at least two high order allocations.

Signed-off-by: Alexander Shishkin <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Kaixu Xia <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Robert Richter <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/1421237903-181015-5-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Alexander Shishkin 2015-01-14 14:18:13 +02:00 • committed by Ingo Molnar
commit 6a27923039
2 changed files with 15 additions and 1 deletions
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15
kernel/events/ring_buffer.c
View file

@ -287,13 +287,26 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
if (!has_aux(event))
return -ENOTSUPP;
if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG)
if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
/*
* We need to start with the max_order that fits in nr_pages,
* not the other way around, hence ilog2() and not get_order.
*/
max_order = ilog2(nr_pages);
/*
* PMU requests more than one contiguous chunks of memory
* for SW double buffering
*/
if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_SW_DOUBLEBUF) &&
!overwrite) {
if (!max_order)
return -EINVAL;
max_order--;
}
}
rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node);
if (!rb->aux_pages)
return -ENOMEM;