From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C204B604DE; Tue, 23 Jan 2024 01:51:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705974691; cv=none; b=BgH2AjW0x380qwfp24y7PjttUBEU2zsktqzq+apDFh4Hhhj+41HD0aWLANCxpdhVZlH0Am+TdvIjzIkAzy14rFva6/rhKcAu9tVaE+0V9LOcP/OrBdKArnblCW1M0J2mZscC2pbUy9esCX6rmCAxsluXQgdZeSRhPt4dAHBlcVA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705974691; c=relaxed/simple; bh=kZ//05DPThWiy81+tkWpQaV0F8ucv5hnC2oeHbqVZEg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tI/SLYR+eQtBRdkAUdXYL8X6f/paKtlWZCq9gsVzLRwH4XV+LnSUYAwRaJ7DK0yr8UIe48kfnZrUC++z9jfCeUVwW5fB10mE9p/AZ5xcCvpBT3AEJXG1eztUI6yZGgwga4foE2wB0PzNd826T+V8L042J/SGHMjOk4TtZB0ZuwM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=nWpLbgJ+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="nWpLbgJ+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81F27C433F1; Tue, 23 Jan 2024 01:51:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1705974691; bh=kZ//05DPThWiy81+tkWpQaV0F8ucv5hnC2oeHbqVZEg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nWpLbgJ+j+NRGUjaJaElkFHxRETmauGtMpC/cu9HIypdLYZswuWqBddKChLslQ5aT PJXVxzeKvpEiFjNSQiWyuWg5KlF3/CIqX6Onmtw7Y8qaVgltEDMUzfGUZBOmvZ7KfK u1/e7wExNsY5+hvwKWejdy3rqzF035+LdKZhbJL4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Gerald Schaefer , Heiko Carstens , Thomas Gleixner , Frederic Weisbecker Subject: [PATCH 5.15 252/374] tick-sched: Fix idle and iowait sleeptime accounting vs CPU hotplug Date: Mon, 22 Jan 2024 15:58:28 -0800 Message-ID: <20240122235753.537690434@linuxfoundation.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240122235744.598274724@linuxfoundation.org> References: <20240122235744.598274724@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Heiko Carstens commit 71fee48fb772ac4f6cfa63dbebc5629de8b4cc09 upstream. When offlining and onlining CPUs the overall reported idle and iowait times as reported by /proc/stat jump backward and forward: cpu 132 0 176 225249 47 6 6 21 0 0 cpu0 80 0 115 112575 33 3 4 18 0 0 cpu1 52 0 60 112673 13 3 1 2 0 0 cpu 133 0 177 226681 47 6 6 21 0 0 cpu0 80 0 116 113387 33 3 4 18 0 0 cpu 133 0 178 114431 33 6 6 21 0 0 <---- jump backward cpu0 80 0 116 114247 33 3 4 18 0 0 cpu1 52 0 61 183 0 3 1 2 0 0 <---- idle + iowait start with 0 cpu 133 0 178 228956 47 6 6 21 0 0 <---- jump forward cpu0 81 0 117 114929 33 3 4 18 0 0 Reason for this is that get_idle_time() in fs/proc/stat.c has different sources for both values depending on if a CPU is online or offline: - if a CPU is online the values may be taken from its per cpu tick_cpu_sched structure - if a CPU is offline the values are taken from its per cpu cpustat structure The problem is that the per cpu tick_cpu_sched structure is set to zero on CPU offline. See tick_cancel_sched_timer() in kernel/time/tick-sched.c. Therefore when a CPU is brought offline and online afterwards both its idle and iowait sleeptime will be zero, causing a jump backward in total system idle and iowait sleeptime. In a similar way if a CPU is then brought offline again the total idle and iowait sleeptimes will jump forward. It looks like this behavior was introduced with commit 4b0c0f294f60 ("tick: Cleanup NOHZ per cpu data on cpu down"). This was only noticed now on s390, since we switched to generic idle time reporting with commit be76ea614460 ("s390/idle: remove arch_cpu_idle_time() and corresponding code"). Fix this by preserving the values of idle_sleeptime and iowait_sleeptime members of the per-cpu tick_sched structure on CPU hotplug. Fixes: 4b0c0f294f60 ("tick: Cleanup NOHZ per cpu data on cpu down") Reported-by: Gerald Schaefer Signed-off-by: Heiko Carstens Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lore.kernel.org/r/20240115163555.1004144-1-hca@linux.ibm.com Signed-off-by: Greg Kroah-Hartman --- kernel/time/tick-sched.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -1528,13 +1528,18 @@ void tick_setup_sched_timer(void) void tick_cancel_sched_timer(int cpu) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + ktime_t idle_sleeptime, iowait_sleeptime; # ifdef CONFIG_HIGH_RES_TIMERS if (ts->sched_timer.base) hrtimer_cancel(&ts->sched_timer); # endif + idle_sleeptime = ts->idle_sleeptime; + iowait_sleeptime = ts->iowait_sleeptime; memset(ts, 0, sizeof(*ts)); + ts->idle_sleeptime = idle_sleeptime; + ts->iowait_sleeptime = iowait_sleeptime; } #endif