From: Yabin Cui Date: Thu, 8 May 2025 23:26:42 +0000 (-0700) Subject: perf/aux: Allocate non-contiguous AUX pages by default X-Git-Tag: v6.16-rc1~196^2~21 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=18049c8cff9cc89daadc4df6975f7d9069638926;p=thirdparty%2Fkernel%2Flinux.git 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: Yabin Cui Signed-off-by: Ingo Molnar Reviewed-by: James Clark Reviewed-by: Anshuman Khandual Cc: Peter Zijlstra Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Alexander Shishkin Cc: Mark Rutland Cc: Namhyung Kim Link: https://lore.kernel.org/r/20250508232642.148767-1-yabinc@google.com --- diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c index fa37565f64186..25ead919fc489 100644 --- a/arch/x86/events/intel/pt.c +++ b/arch/x86/events/intel/pt.c @@ -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 | diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 947ad12dfdbe4..a96c00e2ceca7 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -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 diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 5130b119d0ae0..d2aef87c7e9f8 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -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, @@ -698,16 +706,19 @@ 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; }