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 605BC28D83F for ; Fri, 2 Jan 2026 15:52:57 +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=1767369178; cv=none; b=cgVeEgvPCIeIxOsDFQkQb6sBEWwMScmebfBxG194ubgp3/UFlp9D5FfPib145pDF7kjLYNih0MBwch0wgBvhdxlbWkOp6m6aAqQfB8Y0DajE7H/tWoO89J7o1fSaBRW7auJOchqWAAFYJZMcfvFG9d2ydQGq3aZ07sOegTHDvGI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767369178; c=relaxed/simple; bh=TiQy5vyrKknk6z8OI9Eqlkk0Oo35jrfZ68IPh0/+ysE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=obIiYzVcMAirLszhFgXnsT6WM2ewpEe2rL49xF4peFxIF2heI9gfYDvssPTrvS9/vI66/b8rXW0jsf8hiIDjQ3ODL0oJJfxELC8sUrwXOyQRj3zlaQtTr9t/qBU5r7k2ZCGq3JGC3zA1zSabgzEg7XMyu/z9+VhWFJRymEsxLw8= 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; 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 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 C18E6497; Fri, 2 Jan 2026 07:52:49 -0800 (PST) Received: from [10.57.46.201] (unknown [10.57.46.201]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 98DD43F63F; Fri, 2 Jan 2026 07:52:55 -0800 (PST) Message-ID: <756efd17-682f-4ffc-b8d9-dbb2517bc152@arm.com> Date: Fri, 2 Jan 2026 16:52:53 +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/fair: Reimplement NEXT_BUDDY to align with EEVDF goals To: Ryan Roberts , Mel Gorman , "Peter Zijlstra (Intel)" Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Aishwarya TCV References: <20251112122521.1331238-3-mgorman@techsingularity.net> <176339661525.498.7070393041762616565.tip-bot2@tip-bot2> <4b96909a-f1ac-49eb-b814-97b8adda6229@arm.com> From: Dietmar Eggemann Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 02.01.26 13:38, Ryan Roberts wrote: > Hi, I appreciate I sent this report just before Xmas so most likely you haven't > had a chance to look, but wanted to bring it back to the top of your mailbox in > case it was missed. > > Happy new year! > > Thanks, > Ryan > > On 22/12/2025 10:57, Ryan Roberts wrote: >> Hi Mel, Peter, >> >> We are building out a kernel performance regression monitoring lab at Arm, and >> I've noticed some fairly large perofrmance regressions in real-world workloads, >> for which bisection has fingered this patch. >> >> We are looking at performance changes between v6.18 and v6.19-rc1, and by >> reverting this patch on top of v6.19-rc1 many regressions are resolved. (We plan >> to move the testing to linux-next over the next couple of quarters so hopefully >> we will be able to deliver this sort of news prior to merging in future). >> >> All testing is done on AWS Graviton3 (arm64) bare metal systems. (R)/(I) mean >> statistically significant regression/improvement, where "statistically >> significant" means the 95% confidence intervals do not overlap". You mentioned that you reverted this patch 'patch 2/2 'sched/fair: Reimplement NEXT_BUDDY to align with EEVDF goals'. Does this mean NEXT_BUDDY is still enabled, i.e. you haven't reverted patch 1/2 'sched/fair: Enable scheduler feature NEXT_BUDDY' as well? --- Mel mentioned that he tested on a 2-socket machine. So I guess something like my Intel Xeon Silver 4314: cpu0 0 0 domain0 SMT 00000001,00000001 domain1 MC 55555555,55555555 domain2 NUMA ffffffff,ffffffff node distances: node 0 1 0: 10 20 1: 20 10 Whereas I assume the Graviton3 has 64 CPUs (cores) flat in a single MC domain? I guess topology has influence in benchmark numbers here as well. --- There was also a lot of improvement on schbench (wakeup latency) on higher percentiles (>= 99.0th) on the 2-socket machine with those 2 patches. I guess you haven't seen those on Grav3? [...]