From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F0E6C43334 for ; Mon, 13 Jun 2022 08:55:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229533AbiFMIz3 (ORCPT ); Mon, 13 Jun 2022 04:55:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59346 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239397AbiFMIn0 (ORCPT ); Mon, 13 Jun 2022 04:43:26 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15E97C45; Mon, 13 Jun 2022 01:43:26 -0700 (PDT) Date: Mon, 13 Jun 2022 08:43:23 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1655109804; 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=PHjuPIMbgdG2lR+qQVtbOKhjK916xLaRY2n9UJBw2Cs=; b=3n1AJdDxkYWxTvX4BubnRkoE5gGX5CHyTSD3JnTUGC5/C2IO2BOzvvIWwQk9S3zsDOiZF5 rD3S7SRmDKRBNueFnmMfszfZMYOtQ4XrSZvzpNqp7/DkmGAnq5tM13l5gnHuwxY2WZNchW RXsfsCjj/HWOqJjWQF+OcUON16++oT5E4wFfkV9rQMbgezp2L0fYGPJDWa2M0wyXD5pN3o eOD1IfZf1k2Fql2T41JV5xhuxvd3AXSpeAozllHSO4fxjRB5m7Af5mod11tIT61bfiiYGg hgdJxep1dlrYD9I+HjB/0w9VfcUaV2treEOKGxMBU4XmPTbaoLR3DZiSdQopOw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1655109804; 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=PHjuPIMbgdG2lR+qQVtbOKhjK916xLaRY2n9UJBw2Cs=; b=N6P2/Y+gsKq1Uj2HVSh/ousT7E8uMViHXs1BGeRQOR5mzfW32TXfx+SvyiK5/JtwGN5r6b HzPuQ1MLQM/gVWDg== From: "tip-bot2 for Tianchen Ding" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: Fix the check of nr_running at queue wakelist Cc: Valentin Schneider , Tianchen Ding , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20220608233412.327341-2-dtcccc@linux.alibaba.com> References: <20220608233412.327341-2-dtcccc@linux.alibaba.com> MIME-Version: 1.0 Message-ID: <165510980360.4207.9149154297957353437.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 28156108fecb1f808b21d216e8ea8f0d205a530c Gitweb: https://git.kernel.org/tip/28156108fecb1f808b21d216e8ea8f0d205a530c Author: Tianchen Ding AuthorDate: Thu, 09 Jun 2022 07:34:11 +08:00 Committer: Peter Zijlstra CommitterDate: Mon, 13 Jun 2022 10:30:01 +02:00 sched: Fix the check of nr_running at queue wakelist The commit 2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling") checked rq->nr_running <= 1 to avoid task stacking when WF_ON_CPU. Per the ordering of writes to p->on_rq and p->on_cpu, observing p->on_cpu (WF_ON_CPU) in ttwu_queue_cond() implies !p->on_rq, IOW p has gone through the deactivate_task() in __schedule(), thus p has been accounted out of rq->nr_running. As such, the task being the only runnable task on the rq implies reading rq->nr_running == 0 at that point. The benchmark result is in [1]. [1] https://lore.kernel.org/all/e34de686-4e85-bde1-9f3c-9bbc86b38627@linux.alibaba.com/ Suggested-by: Valentin Schneider Signed-off-by: Tianchen Ding Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Link: https://lore.kernel.org/r/20220608233412.327341-2-dtcccc@linux.alibaba.com --- kernel/sched/core.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bfa7452..294b918 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3829,8 +3829,12 @@ static inline bool ttwu_queue_cond(int cpu, int wake_flags) * CPU then use the wakelist to offload the task activation to * the soon-to-be-idle CPU as the current CPU is likely busy. * nr_running is checked to avoid unnecessary task stacking. + * + * Note that we can only get here with (wakee) p->on_rq=0, + * p->on_cpu can be whatever, we've done the dequeue, so + * the wakee has been accounted out of ->nr_running. */ - if ((wake_flags & WF_ON_CPU) && cpu_rq(cpu)->nr_running <= 1) + if ((wake_flags & WF_ON_CPU) && !cpu_rq(cpu)->nr_running) return true; return false;