From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f174.google.com (mail-pl1-f174.google.com [209.85.214.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B100631CA54 for ; Mon, 10 Nov 2025 16:37:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762792681; cv=none; b=GuUDLGSfFiY+8AqeNGVrIBnsuIugXO5I4DRGPcBA2r4DXkCryAsqohUAZJ1oHztDSqTR3DtjWeSrol2ACNg6fChCwXNu4/d6Ha5PRaFiR36CgmCvGRkUGfmOlH9bJViay0XvOWhA7Ux8oHpZKvu0Dj6DCzX2+G66njSxHu+qOvY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762792681; c=relaxed/simple; bh=u5rYMDHG15I/cQVc25duuIIeZNrf7utvrw96eXmgPSk=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MqEbdFQNENgyCZhylhRLWPCKEYfQozLXq3QM0K8Gx7+Klkwm2TmbuI3GL0YYbzFuH/Uz+shQZhpZZDlyOcP1JYmshqe6GVTgJN2F0bH0qKFaF+WApnRiohMf8hr9WrsvHlwlBBUIvvc/i4vT850KkHnWcGBvqG2yy3mXX2NrIdg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=jgN9V9tb; arc=none smtp.client-ip=209.85.214.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jgN9V9tb" Received: by mail-pl1-f174.google.com with SMTP id d9443c01a7336-29808a9a96aso13788485ad.1 for ; Mon, 10 Nov 2025 08:37:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1762792678; x=1763397478; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:from:to:cc:subject:date:message-id :reply-to; bh=IoYSCz9IZK+WTJVuSJ5kdqWuXYPyBcWSfVrsNGbuyIk=; b=jgN9V9tb1u2tX7EcLEJaOx8wVnAL8EdgrCnutPFBySuBe8TpcwF87l5bJQ05kv654B cRBwwUb7OcQ7aIzhsfrlsliFBLo+mwAO5bOIlAw7pABQSI22M5im1O7UsvfKKD3WPfIJ 59xFuyiMRLSjUHiX/zWvMP2hKOzl+W18Lnibp77oIjYHMuf3ocBNME5HXl/QBIR8TG38 z5fbBv+NGAXzYegr+TiiKlsjv9X0bCCDte2sTBJoL0gQAW8uoroPTAyGJq+iDottAPrO tUBL6mSsNOp2nUNd7s6m6GAnbNxJn8IRlo3LS6O248uqL8YUtliE1kDCunYS4RDkHcgr 1YwA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1762792678; x=1763397478; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:x-gm-gg:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=IoYSCz9IZK+WTJVuSJ5kdqWuXYPyBcWSfVrsNGbuyIk=; b=Jsg3nQ2vbpF0cer81/I8NLfU9FzFWpYEvL3OgdpME8pykfGaxzwqNeQLZ/BCG9+Ps/ joqSBgcAKGH9kgTbtffjzKK9a4PIQbB4nIAtth5ncrhXOMmOdCfdFnEIkiqh9UhA9wlL oeivSCnNuiDHfgfo45ziKPEvkHedZsXQBhjE1ThPZQ/DzP58Cv9eGJVNv7k6t1Y5pFK0 d1uwRUI1OekJrAdMY02B3ouPTrb+Up52AebDXMIpX+ZHaUOr7r6ScAb3e59ir7AmZciX Ctb2RWw1yn50QSC3pbEV8LpbF2PVXgpxnmDyi7YrBoVeIPtqF05wnrHwjgalA+mSCpj0 WBgg== X-Forwarded-Encrypted: i=1; AJvYcCUO1bkjBs3ssaXosdhww3dypjSJlOtcoPjbmrdrB892swnU+53H0dZcf4vaynoKU8jy7qAwX/coIPJ8jQcNuWQG@vger.kernel.org X-Gm-Message-State: AOJu0YyQ56NGzCztBxST9AyErKeVQxyVwOTHsaDIUHkvfgm2QT17dZ0E p+pqMeSs1yi5/RxMP0KHIxuP2x+ftJiaHfKMiscJRVpXBToWjF1TwUb9 X-Gm-Gg: ASbGncs8xzPD9apA4wZCk0htDvrY3cWcL6QLm3Z391RqtPbz8X8hvHiLzxaGpGLWvEG vwPKYX6zogtciEwyMEf7gdGsRSkRQk2GPmwR3J1dM2zz3vQnBRZtbWQK+F0aQ/W4wqMrI/I5qx3 9peYhOkEbrs4aY7jngdEMKkz1bRFOImQWpaBOFv65dwV2W8OjZpSJwkyRb4axo3ene+pspvNaJX H5NET/rpimHlB9NRgWDELdivelFr+C3KrD7lwuOcLTP/cD4YSRlM2dT3D4pZSfBFvZlOiTwHvNv YDqkQLjwVnKPMbiDUndDaPGxAMGemPvpHjRcCihzuhJB7EZR+TR06/61IrxCJ+YwYas0lnOuPgy KhTV72V3NC2GnesjAF8AIlrsmw2HZlvxoU8t7ec86gMtIk1XYJw+fJnwe65m0FWaIqkgmjLo+RF NHbrrpbXv9Tjw= X-Google-Smtp-Source: AGHT+IGNkULY4KbMreL+r3C6zKYa6LAZ6HejhCC3QQjkk4WrB7CidoZ7O068kW/SdXYru/ivG/AiRg== X-Received: by 2002:a17:902:e80e:b0:271:479d:3de2 with SMTP id d9443c01a7336-297e5624c9fmr126791755ad.13.1762792677804; Mon, 10 Nov 2025 08:37:57 -0800 (PST) Received: from localhost ([103.88.46.62]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29651ccec88sm150510135ad.107.2025.11.10.08.37.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Nov 2025 08:37:57 -0800 (PST) From: Jinchao Wang To: Andrew Morton , "Masami Hiramatsu (Google)" , Peter Zijlstra , Randy Dunlap , Marco Elver , Mike Rapoport , Alexander Potapenko , Adrian Hunter , Alexander Shishkin , Alice Ryhl , Andrey Konovalov , Andrey Ryabinin , Andrii Nakryiko , Ard Biesheuvel , Arnaldo Carvalho de Melo , Ben Segall , Bill Wendling , Borislav Petkov , Catalin Marinas , Dave Hansen , David Hildenbrand , David Kaplan , "David S. Miller" , Dietmar Eggemann , Dmitry Vyukov , "H. Peter Anvin" , Ian Rogers , Ingo Molnar , James Clark , Jinchao Wang , Jinjie Ruan , Jiri Olsa , Jonathan Corbet , Juri Lelli , Justin Stitt , kasan-dev@googlegroups.com, Kees Cook , "Liam R. Howlett" , "Liang Kan" , Linus Walleij , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Lorenzo Stoakes , Mark Rutland , Masahiro Yamada , Mathieu Desnoyers , Mel Gorman , Michal Hocko , Miguel Ojeda , Nam Cao , Namhyung Kim , Nathan Chancellor , Naveen N Rao , Nick Desaulniers , Rong Xu , Sami Tolvanen , Steven Rostedt , Suren Baghdasaryan , Thomas Gleixner , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= , Valentin Schneider , Vincent Guittot , Vincenzo Frascino , Vlastimil Babka , Will Deacon , workflows@vger.kernel.org, x86@kernel.org Subject: [PATCH v8 17/27] mm/ksw: add KSTACKWATCH_PROFILING to measure probe cost Date: Tue, 11 Nov 2025 00:36:12 +0800 Message-ID: <20251110163634.3686676-18-wangjinchao600@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251110163634.3686676-1-wangjinchao600@gmail.com> References: <20251110163634.3686676-1-wangjinchao600@gmail.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit CONFIG_KSTACKWATCH_PROFILING enables runtime measurement of KStackWatch probe latencies. When profiling is enabled, KStackWatch collects entry/exit latencies in its probe callbacks. When KStackWatch is disabled by clearing its config file, the previously collected statistics are printed. Signed-off-by: Jinchao Wang --- mm/kstackwatch/Kconfig | 10 +++ mm/kstackwatch/stack.c | 185 ++++++++++++++++++++++++++++++++++++++--- 2 files changed, 183 insertions(+), 12 deletions(-) diff --git a/mm/kstackwatch/Kconfig b/mm/kstackwatch/Kconfig index 496caf264f35..3c9385a15c33 100644 --- a/mm/kstackwatch/Kconfig +++ b/mm/kstackwatch/Kconfig @@ -12,3 +12,13 @@ config KSTACKWATCH introduce minor overhead during runtime monitoring. If unsure, say N. + +config KSTACKWATCH_PROFILING + bool "KStackWatch profiling" + depends on KSTACKWATCH + help + Measure probe latency and overhead in KStackWatch. It records + entry/exit probe times (ns and cycles) and shows statistics when + stopping. Useful for performance tuning, not for production use. + + If unsure, say N. diff --git a/mm/kstackwatch/stack.c b/mm/kstackwatch/stack.c index 3455d1e70db9..72ae2d3adeec 100644 --- a/mm/kstackwatch/stack.c +++ b/mm/kstackwatch/stack.c @@ -6,7 +6,10 @@ #include #include #include +#include +#include #include +#include #define MAX_CANARY_SEARCH_STEPS 128 static struct kprobe entry_probe; @@ -15,6 +18,120 @@ static struct fprobe exit_probe; static bool probe_enable; static u16 probe_generation; +#ifdef CONFIG_KSTACKWATCH_PROFILING +struct measure_data { + u64 total_entry_with_watch_ns; + u64 total_entry_with_watch_cycles; + u64 total_entry_without_watch_ns; + u64 total_entry_without_watch_cycles; + u64 total_exit_with_watch_ns; + u64 total_exit_with_watch_cycles; + u64 total_exit_without_watch_ns; + u64 total_exit_without_watch_cycles; + u64 entry_with_watch_count; + u64 entry_without_watch_count; + u64 exit_with_watch_count; + u64 exit_without_watch_count; +}; + +static DEFINE_PER_CPU(struct measure_data, measure_stats); + +struct measure_ctx { + u64 ns_start; + u64 cycles_start; +}; + +static __always_inline void measure_start(struct measure_ctx *ctx) +{ + ctx->ns_start = ktime_get_ns(); + ctx->cycles_start = get_cycles(); +} + +static __always_inline void measure_end(struct measure_ctx *ctx, u64 *total_ns, + u64 *total_cycles, u64 *count) +{ + u64 ns_end = ktime_get_ns(); + u64 c_end = get_cycles(); + + *total_ns += ns_end - ctx->ns_start; + *total_cycles += c_end - ctx->cycles_start; + (*count)++; +} + +static void show_measure_stats(void) +{ + int cpu; + struct measure_data sum = {}; + + for_each_possible_cpu(cpu) { + struct measure_data *md = per_cpu_ptr(&measure_stats, cpu); + + sum.total_entry_with_watch_ns += md->total_entry_with_watch_ns; + sum.total_entry_with_watch_cycles += + md->total_entry_with_watch_cycles; + sum.total_entry_without_watch_ns += + md->total_entry_without_watch_ns; + sum.total_entry_without_watch_cycles += + md->total_entry_without_watch_cycles; + + sum.total_exit_with_watch_ns += md->total_exit_with_watch_ns; + sum.total_exit_with_watch_cycles += + md->total_exit_with_watch_cycles; + sum.total_exit_without_watch_ns += + md->total_exit_without_watch_ns; + sum.total_exit_without_watch_cycles += + md->total_exit_without_watch_cycles; + + sum.entry_with_watch_count += md->entry_with_watch_count; + sum.entry_without_watch_count += md->entry_without_watch_count; + sum.exit_with_watch_count += md->exit_with_watch_count; + sum.exit_without_watch_count += md->exit_without_watch_count; + } + +#define AVG(ns, cnt) ((cnt) ? ((ns) / (cnt)) : 0ULL) + + pr_info("entry (with watch): %llu ns, %llu cycles (%llu samples)\n", + AVG(sum.total_entry_with_watch_ns, sum.entry_with_watch_count), + AVG(sum.total_entry_with_watch_cycles, + sum.entry_with_watch_count), + sum.entry_with_watch_count); + + pr_info("entry (without watch): %llu ns, %llu cycles (%llu samples)\n", + AVG(sum.total_entry_without_watch_ns, + sum.entry_without_watch_count), + AVG(sum.total_entry_without_watch_cycles, + sum.entry_without_watch_count), + sum.entry_without_watch_count); + + pr_info("exit (with watch): %llu ns, %llu cycles (%llu samples)\n", + AVG(sum.total_exit_with_watch_ns, sum.exit_with_watch_count), + AVG(sum.total_exit_with_watch_cycles, + sum.exit_with_watch_count), + sum.exit_with_watch_count); + + pr_info("exit (without watch): %llu ns, %llu cycles (%llu samples)\n", + AVG(sum.total_exit_without_watch_ns, + sum.exit_without_watch_count), + AVG(sum.total_exit_without_watch_cycles, + sum.exit_without_watch_count), + sum.exit_without_watch_count); +} + +static void reset_measure_stats(void) +{ + int cpu; + + for_each_possible_cpu(cpu) { + struct measure_data *md = per_cpu_ptr(&measure_stats, cpu); + + memset(md, 0, sizeof(*md)); + } + + pr_info("measure stats reset.\n"); +} + +#endif + static void ksw_reset_ctx(void) { struct ksw_ctx *ctx = ¤t->ksw_ctx; @@ -159,25 +276,28 @@ static void ksw_stack_entry_handler(struct kprobe *p, struct pt_regs *regs, unsigned long flags) { struct ksw_ctx *ctx = ¤t->ksw_ctx; - ulong stack_pointer; - ulong watch_addr; + ulong stack_pointer, watch_addr; u16 watch_len; int ret; +#ifdef CONFIG_KSTACKWATCH_PROFILING + struct measure_ctx m; + struct measure_data *md = this_cpu_ptr(&measure_stats); + bool watched = false; + + measure_start(&m); +#endif stack_pointer = kernel_stack_pointer(regs); - /* - * triggered more than once, may be in a loop - */ if (ctx->wp && ctx->sp == stack_pointer) - return; + goto out; if (!ksw_stack_check_ctx(true)) - return; + goto out; ret = ksw_watch_get(&ctx->wp); if (ret) - return; + goto out; ret = ksw_stack_prepare_watch(regs, ksw_get_config(), &watch_addr, &watch_len); @@ -185,17 +305,32 @@ static void ksw_stack_entry_handler(struct kprobe *p, struct pt_regs *regs, ksw_watch_off(ctx->wp); ctx->wp = NULL; pr_err("failed to prepare watch target: %d\n", ret); - return; + goto out; } ret = ksw_watch_on(ctx->wp, watch_addr, watch_len); if (ret) { pr_err("failed to watch on depth:%d addr:0x%lx len:%u %d\n", ksw_get_config()->depth, watch_addr, watch_len, ret); - return; + goto out; } ctx->sp = stack_pointer; +#ifdef CONFIG_KSTACKWATCH_PROFILING + watched = true; +#endif + +out: +#ifdef CONFIG_KSTACKWATCH_PROFILING + if (watched) + measure_end(&m, &md->total_entry_with_watch_ns, + &md->total_entry_with_watch_cycles, + &md->entry_with_watch_count); + else + measure_end(&m, &md->total_entry_without_watch_ns, + &md->total_entry_without_watch_cycles, + &md->entry_without_watch_count); +#endif } static void ksw_stack_exit_handler(struct fprobe *fp, unsigned long ip, @@ -203,15 +338,36 @@ static void ksw_stack_exit_handler(struct fprobe *fp, unsigned long ip, struct ftrace_regs *regs, void *data) { struct ksw_ctx *ctx = ¤t->ksw_ctx; +#ifdef CONFIG_KSTACKWATCH_PROFILING + struct measure_ctx m; + struct measure_data *md = this_cpu_ptr(&measure_stats); + bool watched = false; + measure_start(&m); +#endif if (!ksw_stack_check_ctx(false)) - return; + goto out; if (ctx->wp) { ksw_watch_off(ctx->wp); ctx->wp = NULL; ctx->sp = 0; +#ifdef CONFIG_KSTACKWATCH_PROFILING + watched = true; +#endif } + +out: +#ifdef CONFIG_KSTACKWATCH_PROFILING + if (watched) + measure_end(&m, &md->total_exit_with_watch_ns, + &md->total_exit_with_watch_cycles, + &md->exit_with_watch_count); + else + measure_end(&m, &md->total_exit_without_watch_ns, + &md->total_exit_without_watch_cycles, + &md->exit_without_watch_count); +#endif } int ksw_stack_init(void) @@ -239,7 +395,9 @@ int ksw_stack_init(void) unregister_kprobe(&entry_probe); return ret; } - +#ifdef CONFIG_KSTACKWATCH_PROFILING + reset_measure_stats(); +#endif WRITE_ONCE(probe_generation, READ_ONCE(probe_generation) + 1); WRITE_ONCE(probe_enable, true); @@ -252,4 +410,7 @@ void ksw_stack_exit(void) WRITE_ONCE(probe_generation, READ_ONCE(probe_generation) + 1); unregister_fprobe(&exit_probe); unregister_kprobe(&entry_probe); +#ifdef CONFIG_KSTACKWATCH_PROFILING + show_measure_stats(); +#endif } -- 2.43.0