From nobody Wed Feb 11 22:53:25 2026 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (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 3FD21482DA for ; Tue, 18 Jun 2024 21:59:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718747962; cv=none; b=Ggkf+rVankjiUokzHP1RwLkiflDONUuSdwv6c/WS1sXhklPvi1Lf0Yy+nRh/LcL3yE16oC0Bp8N40pyXQG78LDithL24gcXCPO4HdOzmVGBZOwCbDbV2oyoj0Ie7nKfll+j+x8gvjt1VbKSh/CsNAWveSOH3CpNnp8WTSyhtGjs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718747962; c=relaxed/simple; bh=zm1VjWuxosVrdwVjAJrwwt8BO2mJfxlJ4vmwClREYEM=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=Qmr+g7jDod9pELR8LWYXlXJeKevonmhfVSb5dZWgE8NFp1yAYIInvlmGgL5SZn4lUDFCyqDikxvAp5ux3qLs50hwGGnVvYKi0S3rfwl9M4O8E7WsqQgMiXjsiRbjr5OCbiVsCfyyvyHle+liN6QTCS9GpFw4b+mPrsKAN2eiydQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=k28+dmHf; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="k28+dmHf" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2c7c3069f37so5718a91.0 for ; Tue, 18 Jun 2024 14:59:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1718747960; x=1719352760; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=PR/q/l+rF1KRkhTzXDbNoun8qkscu1njT4o+yNkYLE4=; b=k28+dmHfNWTYBNkesjarSmlQgL4JxPeLOS+kDxqK/QJVmvYdRBRMB7DBOXdquNL2iP qqrUNtlrK1PbFMHjaVVOQpJwYS5WWO6Xb1/E1qAs7l9YfqV6/52aLl0tIykGXBo7+a9M EnDdwgDCW9f7tC9R0Qs6puI4sKdQ4l2BVwyCcQgtpqYsVlrHqhdJivF5nqJQ7QCJT5DO i5lUpyffdN2H04DrzuU5WGseAW2VWUfIyTQajPscMnY2TMpDnCW+ZMcZ0anZ91920lGj Oc7rd0rbvaNPhxAdlZGb2CN8FhU/kj9MPu8Tk/z8LqioaSy/Ob4Nhj4WnYPEvMEQT8rV i2kA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1718747960; x=1719352760; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=PR/q/l+rF1KRkhTzXDbNoun8qkscu1njT4o+yNkYLE4=; b=fjqvTfONaNbdu5zTCU/9Wxu5FT+Vn6KUdDfAnfdAh+8DsxiyXFMaM5q+JwdIWXnAAF feSq+kUJ2FdAJyapq14yM9pYR/5En3G787xDVpawam+gVUoBpp+Ud2LjQhlg0jvrpv00 0KSyrwocmhklCmiTGTDTJqHUkDWgqrlT5VSn6HylVBEMI2cSHZL+J+7cFJBCXgYyqKB3 41hDY1xs+UXRtVSlUQ699GRqDjNI09DPxJNWyBCOdCnuVMbIaRH46RuPpjMucov9LpUj HxDovniogUaVtVKveoSsgSmDvlAIm4iUTojYRjGLtIUvGZwFxsVBF6570OcxGPuZMZNn iwpA== X-Gm-Message-State: AOJu0YzPRjnhCsqiE9p8+H839dbKYySGhp47YFR1Q7124EtMMTPaKZQe qRbVNDUGmo14GEt1FoYfN7AdKFcD6fktTU7K/40JRqJxfB8zTpJ8/kfGx9EhwpUKEL6ss7pvyJH ItinUDVeYjb/kroDXqGeqgdbY57swFp4cL9xgTdCjGW74i7BJRcfNExzoqfVfTCk8AVOYR5GArh RQThoJ0bTiN6+Bf9aK7tKfgOZw30kuebTGYTFeB/IXDcLZ X-Google-Smtp-Source: AGHT+IGgLg+DqDmdh74AEadK98VEnNSHprUuW275qJ3Ck/6JtV96pLW1aeH/U9uruDpiZrekwAX5uOOWjIg8 X-Received: from jstultz-noogler2.c.googlers.com ([fda3:e722:ac3:cc00:24:72f4:c0a8:600]) (user=jstultz job=sendgmr) by 2002:a17:90b:808:b0:2c7:6305:990d with SMTP id 98e67ed59e1d1-2c7b57f9b62mr2785a91.2.1718747958436; Tue, 18 Jun 2024 14:59:18 -0700 (PDT) Date: Tue, 18 Jun 2024 14:58:55 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.45.2.627.g7a2c4fd464-goog Message-ID: <20240618215909.4099720-1-jstultz@google.com> Subject: [PATCH] sched: Move psi_account_irqtime() out of update_rq_clock_task() hotpath From: John Stultz To: LKML Cc: John Stultz , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , Johannes Weiner , Suren Baghdasaryan , Chengming Zhou , Thomas Gleixner , Frederic Weisbecker , Qais Yousef , Joel Fernandes , kernel-team@android.com, Jimmy Shiu Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" It was reported that in moving to 6.1, a larger then 10% regression was seen in the performance of clock_gettime(CLOCK_THREAD_CPUTIME_ID,...). Using a simple reproducer, I found: 5.10: 100000000 calls in 24345994193 ns =3D> 243.460 ns per call 100000000 calls in 24288172050 ns =3D> 242.882 ns per call 100000000 calls in 24289135225 ns =3D> 242.891 ns per call 6.1: 100000000 calls in 28248646742 ns =3D> 282.486 ns per call 100000000 calls in 28227055067 ns =3D> 282.271 ns per call 100000000 calls in 28177471287 ns =3D> 281.775 ns per call The cause of this was finally narrowed down to the addition of psi_account_irqtime() in update_rq_clock_task(), in commit 52b1364ba0b1 ("sched/psi: Add PSI_IRQ to track IRQ/SOFTIRQ pressure"). In my initial attempt to resolve this, I leaned towards moving all accounting work out of the clock_gettime() call path, but it wasn't very pretty, so it will have to wait for a later deeper rework. Instead, Peter shared this approach: Rework psi_account_irqtime() to use its own psi_irq_time base for accounting, and move it out of the hotpath, calling it instead from sched_tick() and __schedule(). In testing this, we found the importance of ensuring psi_account_irqtime() is run under the rq_lock, which Johannes Weiner helpfully explained, so also add some lockdep annotations to make that requirement clear. With this change the performance is back in-line with 5.10: 6.1+fix: 100000000 calls in 24297324597 ns =3D> 242.973 ns per call 100000000 calls in 24318869234 ns =3D> 243.189 ns per call 100000000 calls in 24291564588 ns =3D> 242.916 ns per call Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Daniel Bristot de Oliveira Cc: Valentin Schneider Cc: Johannes Weiner Cc: Suren Baghdasaryan Cc: Chengming Zhou Cc: Thomas Gleixner Cc: Frederic Weisbecker Cc: Qais Yousef Cc: Joel Fernandes Cc: kernel-team@android.com Originally-by: Peter Zijlstra Reported-by: Jimmy Shiu Signed-off-by: John Stultz Reviewed-by: Qais Yousef --- kernel/sched/core.c | 7 +++++-- kernel/sched/psi.c | 21 ++++++++++++++++----- kernel/sched/sched.h | 1 + kernel/sched/stats.h | 11 ++++++++--- 4 files changed, 30 insertions(+), 10 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bcf2c4cc0522..59ce0841eb1f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -723,7 +723,6 @@ static void update_rq_clock_task(struct rq *rq, s64 del= ta) =20 rq->prev_irq_time +=3D irq_delta; delta -=3D irq_delta; - psi_account_irqtime(rq->curr, irq_delta); delayacct_irq(rq->curr, irq_delta); #endif #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING @@ -5665,7 +5664,7 @@ void sched_tick(void) { int cpu =3D smp_processor_id(); struct rq *rq =3D cpu_rq(cpu); - struct task_struct *curr =3D rq->curr; + struct task_struct *curr; struct rq_flags rf; unsigned long hw_pressure; u64 resched_latency; @@ -5677,6 +5676,9 @@ void sched_tick(void) =20 rq_lock(rq, &rf); =20 + curr =3D rq->curr; + psi_account_irqtime(rq, curr, NULL); + update_rq_clock(rq); hw_pressure =3D arch_scale_hw_pressure(cpu_of(rq)); update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure); @@ -6737,6 +6739,7 @@ static void __sched notrace __schedule(unsigned int s= ched_mode) ++*switch_count; =20 migrate_disable_switch(rq, prev); + psi_account_irqtime(rq, prev, next); psi_sched_switch(prev, next, !task_on_rq_queued(prev)); =20 trace_sched_switch(sched_mode & SM_MASK_PREEMPT, prev, next, prev_state); diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 7b4aa5809c0f..507d7b8d79af 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -773,6 +773,7 @@ static void psi_group_change(struct psi_group *group, i= nt cpu, enum psi_states s; u32 state_mask; =20 + lockdep_assert_rq_held(cpu_rq(cpu)); groupc =3D per_cpu_ptr(group->pcpu, cpu); =20 /* @@ -991,22 +992,32 @@ void psi_task_switch(struct task_struct *prev, struct= task_struct *next, } =20 #ifdef CONFIG_IRQ_TIME_ACCOUNTING -void psi_account_irqtime(struct task_struct *task, u32 delta) +void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct t= ask_struct *prev) { - int cpu =3D task_cpu(task); + int cpu =3D task_cpu(curr); struct psi_group *group; struct psi_group_cpu *groupc; - u64 now; + u64 now, irq; + s64 delta; =20 if (static_branch_likely(&psi_disabled)) return; =20 - if (!task->pid) + if (!curr->pid) + return; + + lockdep_assert_rq_held(rq); + group =3D task_psi_group(curr); + if (prev && task_psi_group(prev) =3D=3D group) return; =20 now =3D cpu_clock(cpu); + irq =3D irq_time_read(cpu); + delta =3D (s64)(irq - rq->psi_irq_time); + if (delta < 0) + return; + rq->psi_irq_time =3D irq; =20 - group =3D task_psi_group(task); do { if (!group->enabled) continue; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a831af102070..ef20c61004eb 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1126,6 +1126,7 @@ struct rq { =20 #ifdef CONFIG_IRQ_TIME_ACCOUNTING u64 prev_irq_time; + u64 psi_irq_time; #endif #ifdef CONFIG_PARAVIRT u64 prev_steal_time; diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h index 38f3698f5e5b..b02dfc322951 100644 --- a/kernel/sched/stats.h +++ b/kernel/sched/stats.h @@ -110,8 +110,12 @@ __schedstats_from_se(struct sched_entity *se) void psi_task_change(struct task_struct *task, int clear, int set); void psi_task_switch(struct task_struct *prev, struct task_struct *next, bool sleep); -void psi_account_irqtime(struct task_struct *task, u32 delta); - +#ifdef CONFIG_IRQ_TIME_ACCOUNTING +void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct t= ask_struct *prev); +#else +static inline void psi_account_irqtime(struct rq *rq, struct task_struct *= curr, + struct task_struct *prev) {} +#endif /*CONFIG_IRQ_TIME_ACCOUNTING */ /* * PSI tracks state that persists across sleeps, such as iowaits and * memory stalls. As a result, it has to distinguish between sleeps, @@ -192,7 +196,8 @@ static inline void psi_ttwu_dequeue(struct task_struct = *p) {} static inline void psi_sched_switch(struct task_struct *prev, struct task_struct *next, bool sleep) {} -static inline void psi_account_irqtime(struct task_struct *task, u32 delta= ) {} +static inline void psi_account_irqtime(struct rq *rq, struct task_struct *= curr, + struct task_struct *prev) {} #endif /* CONFIG_PSI */ =20 #ifdef CONFIG_SCHED_INFO --=20 2.45.2.627.g7a2c4fd464-goog