From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 0FC2E2EC54C for ; Tue, 10 Feb 2026 18:22:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770747759; cv=none; b=T+Xyh39QNPT0FhOZW17eIW+WIlBF+82K/hfsO2wa2dVNgXZ2NAfcOApLjVK8NmMRAsRTdp+fmXMpFHRvUF10A2g/94TVdf3+dlbtuj4UWpldjpyqdaIK23GzQREAavAjod8x3rnwpGdWmOxyvgg2bQAYUofgjoUt0uPflV+sDps= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770747759; c=relaxed/simple; bh=8LcFHvyTYv9Fk92K63DW5TqYJ2bw9+ULTG8k5cAjMhk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mVPXkc4oX7v0XZK/vaHpzYlS3ky7MsT0GHLRD2glRf5ASx6xOehoGxb0CFIG8PJJ0suQ+DX4JMPJVwlYAMLyKEWK4au6Js5kOgxBr4wtYZRauhm8w4WEwUHXhURSQDu0V8DUvpnEJIxAEPsxaScvjKN6UTPT2hKgHAMeteg0sOk= 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=cPzHFBtM; arc=none smtp.client-ip=90.155.50.34 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="cPzHFBtM" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=DJbDEo75j3+2VOUpodQDOBB79Mmdxz0BnK9+7/uyN+M=; b=cPzHFBtMrAtvXememE9UHcrVKD t70/zr9jFPwDsMgN6I+L+cZOB6zB99iiK14o1mH4C48IPpWMX7YSA7/4+CY4vZagCySTJ7y/yHCUI B49p8NSmxiUb+u3nDRoLYH2wSmn0cjDpagiODGSNKlfLmDGqnkAMtdosKjwbN5MtcKG3PLhqgMv63 YUVwMFz2wU8WfMVDSebp3s07rt+XLkwxyyQnjTc/Ee11bOVL0tycuFqJAgVmuSEW3i+asUu5GnG5W Z0/EVTONu0PrNUjqsMSIp+FDNc4/y1h+6N1sraCudxxjEmxJHX/mWpdj9O9DPArIRE5qsxk5nZtbZ OcN2hdqQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vpsNS-0000000BSoM-0UnW; Tue, 10 Feb 2026 18:22:22 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id D225630075B; Tue, 10 Feb 2026 19:13:08 +0100 (CET) Date: Tue, 10 Feb 2026 19:13:08 +0100 From: Peter Zijlstra To: Doug Smythies Cc: 'K Prateek Nayak' , 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, wuyun.abel@bytedance.com Subject: Re: [PATCH 0/4] sched: Various reweight_entity() fixes Message-ID: <20260210181308.GO2995752@noisy.programming.kicks-ass.net> References: <20260130093439.803225718@infradead.org> <4c48fe59-8ff3-41fb-83cb-869409f6fbc6@amd.com> <20260203111134.GL1282955@noisy.programming.kicks-ass.net> <38ef3462-4c4e-4f40-8d63-84dd71cbd043@amd.com> <004a01dc952b$471c94a0$d555bde0$@telus.net> 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: <004a01dc952b$471c94a0$d555bde0$@telus.net> On Tue, Feb 03, 2026 at 08:36:41AM -0800, Doug Smythies wrote: > Further to my email from the other day, where all was good [1], > I have continued to test, in particular the severe overload conditions > from [2]. > Conditions: > Greater than 12,500 X (yes > /dev/null) tasks > But less than 15,000 X ( yes > /dev/null) tasks > > I have tested up to 20,000 X (yes > /dev/null) tasks > with previous kernels, including mainline 6.19-rc1. > > I would not disagree if you say my operating conditions > are ridiculous. They absolutely are; however!, people do crazy things so I doubt you are alone. > System: > Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs. > CPU frequency scaling driver: intel_pstate; Governor powersave. Right, so I was too lazy to find a matching test machine, but instead used taskset to limit myself to 6 cores/12 threads and let it rip. # taskset -c -p 0-5,24-29 $$ # for ((i=0; i<20000; i++)) do yes > /dev/null & done ... a *LONG* while later ... And I have reached 15k. ... this is *SLOW* ... So I reached 20000 and figured what the heck and went for another 5k. Eventually I managed to reach 21160, and then boom. It is one of those pick_next_task_fair() NULL pointer derefs that are so very indicative of math overflow. I'll try and have a poke, if only this were a faster thing ;-)