From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 8C628307492 for ; Thu, 19 Feb 2026 07:53:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771487609; cv=none; b=esRTtXSpJlItuRWbgKjDSCi8UosANt49gvu53VVpXJm3dgoMGS1fMkNduwKFUJILmYa8htqlGxstel2eYMwGTmxIDTSjEvYjfZe0+xaL9PTh1j55ExqnC3r6HdLvdGL3tXC6bPHMd2yeqwZaJn6XTAp6NwJo/IdX8D1SY8fN7qU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771487609; c=relaxed/simple; bh=ooclBNG864lkTSIN0rrjFbZaIzV2QLiKrqwGzQOBqqM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aUwU5mSQ+jshZ5j4rd/YhbXBL+4NSM7wNeFtYOSrRZ646QSTccHLbSV1yQAeU6bgtuH9zUZcoAOE8QHQlgzNodhI1CT2/lzjImwkRq8LrfN0osEgaetMUdeUkYCjXmoGC5UXCCISwznOjv+m8eLH3q+zWZx8M68TvgTfxxw5xjE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=bF25j48+; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="bF25j48+" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=xYQ2wDRe37hiJYYSYNz6YnmFXKi4vQpQ85reLTVabgQ=; b=bF25j48+ZQU1bDZqcSzeA8ssyw tt81NPO7x1bPpzjjVM4d7jGbHe3Ay5SKolnFMCSS7+Jgsh2/MVwNXKg7i85oCIv74fST4YZBjNYkR yMb7DVPjqpfgmZ4MNae5j3CgSt96j/SqWOhE/2kCzUJ5Pms6/bzmkQBr1vckWEzyRg8Gen5fXkPZT SL2NRO8orvLQD60A99NZM/xR00Xz7pJoH/bAiLArH0rJ+D9IfCHf/+3BUMc62DfCTncp5T+1rGHK6 dT6enL9s4WHKmAJr4fwpL+2vLG47LEIzlq/DEFfFMvzFpMms6IanoVlZsd9IOj2hWST9HxLz4wdGS eAjloyEA==; Received: from 2001-1c00-8d85-5700-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:5700:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vsyqT-00000000woB-2g3s; Thu, 19 Feb 2026 07:53:09 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B917D3011E4; Thu, 19 Feb 2026 08:53:07 +0100 (CET) Date: Thu, 19 Feb 2026 08:53:07 +0100 From: Peter Zijlstra To: Shubhang Kaushik Cc: mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, wangtao554@huawei.com, quzicheng@huawei.com, kprateek.nayak@amd.com, wuyun.abel@bytedance.com, dsmythies@telus.net Subject: Re: [PATCH 0/4] sched: Various reweight_entity() fixes Message-ID: <20260219075307.GD1395266@noisy.programming.kicks-ass.net> References: <20260130093439.803225718@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Feb 18, 2026 at 10:37:19AM -0800, Shubhang Kaushik wrote: > Hello Peter, > > On Fri, 30 Jan 2026, Peter Zijlstra wrote: > > > Two issues related to reweight_entity() were raised; poking at all that got me > > these patches. > > > > They're in queue.git/sched/core and I spend most of yesterday staring at traces > > trying to find anything wrong. So far, so good. > > > > Please test. > > > > > > Analysis of commit bdba3187771c ("sched/fair: Use full weight to > __calc_delta()") confirms it resolves a scaling bottleneck present in the > v7.0-rc baseline (cee73b1e840c). > > On Ampere Altra (80 cores) non-SMT SMP with CONFIG_NOHZ_FULL and > CONFIG_SCHED_CLUSTER enabled, the baseline suffered from vruntime distortion > that caused significant scheduling jitter, resulting in measurable > performance cliffs under high parallel load. > > Llama AIO for Inference Scaling : The baseline shows a performance cliffs at > high thread counts, due to the scheduler miscalculating time slices for tail > threads, which forced the entire synchronous inference batch to wait. The > patch corrects the delta calculation for predictable scaling. > > n_threads Baseline (cee73b1e840c) Patched (bdba3187771c) Diff > 51 8.46 t/s 12.12 t/s +43.3% > 52 17.75 t/s 22.26 t/s +25.4% > 64 12.40 t/s 14.66 t/s +18.2% > > Hackbench scaling in the baseline was non-linear indicating excessive > scheduling overhead as process counts increased. By using the full weight > for delta calculations, the patch reduces unnecessary migrations and > improves message throughput. > > Task Count Baseline(sec) Patched(sec) Throughput > 16 Processes 51.25s 44.09s +16.2% > 32 Processes 92.42s 78.09s +18.3% > > Tested-by: Shubhang Kaushik These are excellent results, thanks! Let me finally get around to posting them.