Commit 18049c8c authored by Yabin Cui's avatar Yabin Cui Committed by Ingo Molnar
Browse files

perf/aux: Allocate non-contiguous AUX pages by default 



perf always allocates contiguous AUX pages based on aux_watermark.
However, this contiguous allocation doesn't benefit all PMUs. For
instance, ARM SPE and TRBE operate with virtual pages, and Coresight
ETR allocates a separate buffer. For these PMUs, allocating contiguous
AUX pages unnecessarily exacerbates memory fragmentation. This
fragmentation can prevent their use on long-running devices.

This patch modifies the perf driver to be memory-friendly by default,
by allocating non-contiguous AUX pages. For PMUs requiring contiguous
pages (Intel BTS and some Intel PT), the existing
PERF_PMU_CAP_AUX_NO_SG capability can be used. For PMUs that don't
require but can benefit from contiguous pages (some Intel PT), a new
capability, PERF_PMU_CAP_AUX_PREFER_LARGE, is added to maintain their
existing behavior.

Signed-off-by: default avatarYabin Cui <yabinc@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarJames Clark <james.clark@linaro.org>
Reviewed-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20250508232642.148767-1-yabinc@google.com
parent 881097c0

arch/x86/events/intel/pt.c

+2 −0
Original line number Diff line number Diff line
@@ -1863,6 +1863,8 @@ static __init int pt_init(void) 


	if (!intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries))

		pt_pmu.pmu.capabilities = PERF_PMU_CAP_AUX_NO_SG;

	else

		pt_pmu.pmu.capabilities = PERF_PMU_CAP_AUX_PREFER_LARGE;



	pt_pmu.pmu.capabilities		|= PERF_PMU_CAP_EXCLUSIVE |

					   PERF_PMU_CAP_ITRACE |

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -303,6 +303,7 @@ struct perf_event_pmu_context; 
#define PERF_PMU_CAP_AUX_OUTPUT			0x0080

#define PERF_PMU_CAP_EXTENDED_HW_TYPE		0x0100

#define PERF_PMU_CAP_AUX_PAUSE			0x0200

#define PERF_PMU_CAP_AUX_PREFER_LARGE		0x0400



/**

 * pmu::scope

kernel/events/ring_buffer.c

+20 −9
Original line number Diff line number Diff line
@@ -679,7 +679,15 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event, 
{

	bool overwrite = !(flags & RING_BUFFER_WRITABLE);

	int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);

	int ret = -ENOMEM, max_order;

	bool use_contiguous_pages = event->pmu->capabilities & (

		PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_AUX_PREFER_LARGE);

	/*

	 * Initialize max_order to 0 for page allocation. This allocates single

	 * pages to minimize memory fragmentation. This is overridden if the

	 * PMU needs or prefers contiguous pages (use_contiguous_pages = true).

	 */

	int max_order = 0;

	int ret = -ENOMEM;



	if (!has_aux(event))

		return -EOPNOTSUPP;
@@ -689,8 +697,8 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event, 


	if (!overwrite) {

		/*

		 * Watermark defaults to half the buffer, and so does the

		 * max_order, to aid PMU drivers in double buffering.

		 * Watermark defaults to half the buffer, to aid PMU drivers

		 * in double buffering.

		 */

		if (!watermark)

			watermark = min_t(unsigned long,
@@ -698,15 +706,18 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event, 
					  (unsigned long)nr_pages << (PAGE_SHIFT - 1));



		/*

		 * Use aux_watermark as the basis for chunking to

		 * help PMU drivers honor the watermark.

		 * If using contiguous pages, use aux_watermark as the basis

		 * for chunking to help PMU drivers honor the watermark.

		 */

		if (use_contiguous_pages)

			max_order = get_order(watermark);

	} else {

		/*

		 * We need to start with the max_order that fits in nr_pages,

		 * not the other way around, hence ilog2() and not get_order.

		 * If using contiguous pages, we need to start with the

		 * max_order that fits in nr_pages, not the other way around,

		 * hence ilog2() and not get_order.

		 */

		if (use_contiguous_pages)

			max_order = ilog2(nr_pages);

		watermark = 0;

	}