Commit 6a279230 authored Jan 14, 2015 by Alexander Shishkin Committed by Ingo Molnar Apr 02, 2015

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



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 <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kaixu Xia <kaixu.xia@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: adrian.hunter@intel.com
Cc: kan.liang@intel.com
Cc: markus.t.metzger@intel.com
Cc: mathieu.poirier@linaro.org
Link: http://lkml.kernel.org/r/1421237903-181015-5-git-send-email-alexander.shishkin@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 0a4e38e6

include/linux/perf_event.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -175,6 +175,7 @@ struct perf_event;
		#define PERF_PMU_CAP_NO_INTERRUPT 0x01
		#define PERF_PMU_CAP_NO_NMI 0x02
		#define PERF_PMU_CAP_AUX_NO_SG 0x04
		#define PERF_PMU_CAP_AUX_SW_DOUBLEBUF 0x08

		/**
		* struct pmu - generic performance monitoring unit

kernel/events/ring_buffer.c

+14 −1

Original line number	Diff line number	Diff line
		@@ -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;

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