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

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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.

Bug: 393467632
(cherry picked from commit 18049c8cff9cc89daadc4df6975f7d9069638926
 git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core)
Change-Id: Iaff554201726bf271c7625a6df59fb35c6cfbc5d
Signed-off-by: Yabin Cui <yabinc@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Anshuman 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
This commit is contained in:
Yabin Cui
2025-05-08 16:26:42 -07:00
parent 33d0bb4218
commit 77a6a96651
3 changed files with 23 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/events/intel/pt.c
View File

@@ -1793,6 +1793,8 @@ 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;
pt_pmu.pmu.attr_groups = pt_attr_groups;

1
include/linux/perf_event.h
View File

@@ -291,6 +291,7 @@ struct perf_event_pmu_context;
#define PERF_PMU_CAP_NO_EXCLUDE 0x0040
#define PERF_PMU_CAP_AUX_OUTPUT 0x0080
#define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0100
#define PERF_PMU_CAP_AUX_PREFER_LARGE 0x0400
struct perf_output_handle;

29
kernel/events/ring_buffer.c
View File

@@ -673,15 +673,23 @@ 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;
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,
@@ -689,16 +697,19 @@ 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.
*/
max_order = get_order(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.
*/
max_order = ilog2(nr_pages);
if (use_contiguous_pages)
max_order = ilog2(nr_pages);
watermark = 0;
}