From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E1E5439B4B9; Mon, 6 Jul 2026 14:29:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783348199; cv=none; b=nAK58Spmp/ZZV2qEIcYQcGHnz7b+4K3+OiJ04EY5ilsVqXM7lMM8eFSs5leIcfw3VwFevpwvkoNK3naoKlKQXri0EXZTmKW+aLr+Tx1uofxWi2kkL/0QPiuwynJ6ADILe9DhnovgUH48/rBU4g0WgQ1BT4F7v5+rKO9fWcMrOEg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783348199; c=relaxed/simple; bh=EHTVXpLQN4gAdnhonC+dqDnLj3DCyY4jhjDQXN2MSiI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UpM9JBP7Pr2LuTuWE2IE9L5xOEtd/LowRQBJiXbZpZIlUSt3szXs8qmknIP4tRiQhm/1AL3w7BcRKrHtatw9NzGGtmBgw1XRACZbVSivGO13iFGf2R08431RtpJxjFgB6M83Vcg9rk5uVz3DtgaDDA6HlcUmKA5L8Ag7KaOq/QE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=HslELLYI; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="HslELLYI" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0DF3A2BCB; Mon, 6 Jul 2026 07:29:53 -0700 (PDT) Received: from [10.1.27.96] (e127648.arm.com [10.1.27.96]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9165B3F905; Mon, 6 Jul 2026 07:29:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783348197; bh=EHTVXpLQN4gAdnhonC+dqDnLj3DCyY4jhjDQXN2MSiI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HslELLYIvlxSEpjExw8Mql4VMl+Zixo9nWuUac3ORv0qmLQ1UuA1F7Dif+aNSG085 yS4/8GRFt2LNuvxll2feRGFKpgYr5u+rsBU5tgcW7l2X4tAH1OhT9lQ9kvk0sB/Xek 2F6OojsHheuTP5kHx9p3dqqDpKjca0vOa/Q6a9G0= Message-ID: <5f5cb821-92ae-4539-ae81-a43e33a7ded5@arm.com> Date: Mon, 6 Jul 2026 15:29:53 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION] sched/idle: Sysbench threads regression after f4c31b07b136 To: "Rafael J. Wysocki (Intel)" , Joseph Salisbury Cc: rafael.j.wysocki@intel.com, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , frederic@kernel.org, linux-pm@vger.kernel.org, LKML , regressions@lists.linux.dev References: <096b42fa-107f-450d-b3b1-03bcad3f1e04@oracle.com> Content-Language: en-US From: Christian Loehle In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/2/26 19:47, Rafael J. Wysocki (Intel) wrote: > Hi, > > On Thu, Jul 2, 2026 at 6:30 PM Joseph Salisbury > wrote: >> >> Hi Rafael, >> >> We are seeing a reproducible MySQL Sysbench threads regression. A >> bisect indicated the following commit as the first bad commit: >> f4c31b07b136 ("sched: idle: Consolidate the handling of two special cases") >> >> The regression was found in Oracle kernel performance testing on OCI VM >> shapes: >> >> VM Details: >> * VM.Standard2.1: >> x86 OCI VM shape, 1 OCPU / 2 hardware threads, about 14.5 GB RAM >> >> * VM.Standard.A1.Flex.2: >> Arm/Ampere A1 flexible VM shape, 2 vCPU threads, about 10.9 GB RAM >> >> >> The ResultsDB runs show the regression in the Sysbench threads metric: >> >> - VM.Standard2.1: 333 -> 236 (-29.1%) >> - VM.Standard.A1.Flex.2: 1286 -> 1152 (-10.4%) >> >> A test kernel was built with f4c31b07b136 reverted and the performance >> regression was recovered. >> >> From the code, it is possible the regression is due to the new >> previous-wakeup heuristic in the special idle cases. Before the commit: >> >> - no cpuidle driver: >> tick_nohz_idle_stop_tick() >> default_idle_call() >> >> - one idle state: >> tick_nohz_idle_retain_tick() >> cpuidle state 0 > > I think that this is your case and the tick stops for you sometimes > now while it had never stopped before. > > Can you confirm? > > Overall, it would be good to know the idle state lists for both the VM > and the host. > +1, but also which HZ are you using? Both systems reported have 2 logical CPUs then? Were higher core counts also tested and how does it affect them?