From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 64BAB208998; Mon, 2 Dec 2024 11:14:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733138092; cv=none; b=F9baT3hfVeZ0Br5EKamgCHnaBehdQ30XxDuUu3R5quiVFuDlpkYyUd7YE2PL2iZNoYCmr+b7cbOeWWOTtJeiXl+HTfjTO3p1NyEwoV9kUcoXvx2fDCIfV6bUd39xCAn4Umlk0PHd8Sytfu9/Td8UaHseisesBTSLX1jBrUCGgKk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733138092; c=relaxed/simple; bh=d9vIAERBPGSf4tcKRkqbW5991dzhPObvzY2mTvsgkSM=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=huSlj+bToKYopdXC+4nzrqpHI75vow2s1on6E52pPwO4hB5Yjjl5i3bWinLGfcg1gxHr6DR0K+wMHzlrUtTVsBSEm6m2DjI+V0AfPBzh+Q4i4tCeen+UEyW/icwOSUDk7oKUxlm34IYjH30nNttRAsnUrO25GvfzcMXxOK086Hw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=t2qFqBOG; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Yw0gzk4J; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="t2qFqBOG"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Yw0gzk4J" Date: Mon, 02 Dec 2024 11:14:48 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1733138089; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YUmMzgoNng+eeMZc/KLTJZP+upNMCB6hRTHIGB1/IHI=; b=t2qFqBOGCSxg8rKRjRkFRSnOFSonlOHYk2w786OnFMXIbZ3ePBp85SnwvHZ4E12sPnDSY4 Kcwwnf3QZpultBLPPDWp7hO6mS89gJOJZJw0jh3aeqa9MRwPUlTf+O6oWZaQ1agmTs6oiz zg1Xehh7pWL9y1NzpXLu9hopEwFmQqBbIl0/z6TuO0yLVYNpuSe5L2GIwdCkoSGS4duFHW r/tFdtbRC+Qjf+x4q/W9+e8eePh/ydOI27N6EjDhaq9RYVlzVjvBGvUyOLIfFNioTbXqQu l6ofCoVVg7stWexEXn0ft5KXv1GOuYNUKJ+P4dh1UiIUiwN4WPM2Ma8MbuBERA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1733138089; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YUmMzgoNng+eeMZc/KLTJZP+upNMCB6hRTHIGB1/IHI=; b=Yw0gzk4JNqFiaiNWnhYAgK9XjG22iWpfGYKoqglNnfO+uIBhwAcFUnDawiC39Jbr34gILf C2+0QGuWFH1UMpDA== From: "tip-bot2 for K Prateek Nayak" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched/core: Prevent wakeup of ksoftirqd during idle load balance Cc: Julia Lawall , Sebastian Andrzej Siewior , K Prateek Nayak , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20241119054432.6405-5-kprateek.nayak@amd.com> References: <20241119054432.6405-5-kprateek.nayak@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <173313808824.412.3339188414358925845.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit The following commit has been merged into the sched/core branch of tip: Commit-ID: e932c4ab38f072ce5894b2851fea8bc5754bb8e5 Gitweb: https://git.kernel.org/tip/e932c4ab38f072ce5894b2851fea8bc5754bb8e5 Author: K Prateek Nayak AuthorDate: Tue, 19 Nov 2024 05:44:32 Committer: Peter Zijlstra CommitterDate: Mon, 02 Dec 2024 12:01:28 +01:00 sched/core: Prevent wakeup of ksoftirqd during idle load balance Scheduler raises a SCHED_SOFTIRQ to trigger a load balancing event on from the IPI handler on the idle CPU. If the SMP function is invoked from an idle CPU via flush_smp_call_function_queue() then the HARD-IRQ flag is not set and raise_softirq_irqoff() needlessly wakes ksoftirqd because soft interrupts are handled before ksoftirqd get on the CPU. Adding a trace_printk() in nohz_csd_func() at the spot of raising SCHED_SOFTIRQ and enabling trace events for sched_switch, sched_wakeup, and softirq_entry (for SCHED_SOFTIRQ vector alone) helps observing the current behavior: -0 [000] dN.1.: nohz_csd_func: Raising SCHED_SOFTIRQ from nohz_csd_func -0 [000] dN.4.: sched_wakeup: comm=ksoftirqd/0 pid=16 prio=120 target_cpu=000 -0 [000] .Ns1.: softirq_entry: vec=7 [action=SCHED] -0 [000] .Ns1.: softirq_exit: vec=7 [action=SCHED] -0 [000] d..2.: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=ksoftirqd/0 next_pid=16 next_prio=120 ksoftirqd/0-16 [000] d..2.: sched_switch: prev_comm=ksoftirqd/0 prev_pid=16 prev_prio=120 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120 ... Use __raise_softirq_irqoff() to raise the softirq. The SMP function call is always invoked on the requested CPU in an interrupt handler. It is guaranteed that soft interrupts are handled at the end. Following are the observations with the changes when enabling the same set of events: -0 [000] dN.1.: nohz_csd_func: Raising SCHED_SOFTIRQ for nohz_idle_balance -0 [000] dN.1.: softirq_raise: vec=7 [action=SCHED] -0 [000] .Ns1.: softirq_entry: vec=7 [action=SCHED] No unnecessary ksoftirqd wakeups are seen from idle task's context to service the softirq. Fixes: b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()") Closes: https://lore.kernel.org/lkml/fcf823f-195e-6c9a-eac3-25f870cb35ac@inria.fr/ [1] Reported-by: Julia Lawall Suggested-by: Sebastian Andrzej Siewior Signed-off-by: K Prateek Nayak Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/20241119054432.6405-5-kprateek.nayak@amd.com --- kernel/sched/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 803b238..c6d8232 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1285,7 +1285,7 @@ static void nohz_csd_func(void *info) rq->idle_balance = idle_cpu(cpu); if (rq->idle_balance) { rq->nohz_idle_balance = flags; - raise_softirq_irqoff(SCHED_SOFTIRQ); + __raise_softirq_irqoff(SCHED_SOFTIRQ); } }