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 3AABB4248CB for ; Tue, 28 Jul 2026 10:49:02 +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=1785235746; cv=none; b=tXz69pIH/qWBo2nMT1u1S1rsNBgywBGSRx2JspeUC0dkywVgwqWpsB6mDAbqHpL+hyNVx8UmGiFyTMiK2GTy3OJeNIoaqsu9w9lguPIGtTxWMdRVImUwRGH8vF2Dqy+K9ylx6GtwmhLLT7X4QDbA51nRF7CKleZX2x7r1jnOuKs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785235746; c=relaxed/simple; bh=iV2qkQC2sV1D4wFekOTirfG8m7FQgA0mcSS7p/9A4sE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uxt6J0FMvMjBfGVSPweFplMW0ZTMDgdI6k4o1B3HUkRrhkdPkP1N2bWWkslpY+B0OT7D60xSBLYKplsL5AZVVNAFFfe8h6/BadrlS0G1oFlEMwf6f6TmrbzRdG2EM5TIajrHeD5u/z/sxT60mIHs9jeJhZnc/waD2rQrS8/KgpQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=J4He7l6+; 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=pass 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="J4He7l6+" 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=SDvwep0jk/cCgIlCnTdrSrbHhxIH7trbK/13KQDqnxc=; b=J4He7l6+D5J6YIaqBO2hm+WSDy VvKG2gPZXQtzJ332wruDmrtSsVPHRmYu5yU6BVezf8tZz6xomJT9briHM3MS1VKIWvVZzkjJpdCi0 kHIybZWoX3cNZ789DRBTZBXCra4hsKr+BSKJo031oWnd2ueQD21ebpbdnVpbOfQRdC6XiQ7Jdn58s q0ncl1L0+1akTHnzU8TzTVQdJL3emKe5phROqWP8MA9l4F8O5xADuGQ6YXSL2lu7zWCRNtfO33BYv bIORwASs70eP/9yttEGnKfcmp4z6MV8F4nf0dt8SuWbLSEOeMB5xbyxZhsgAJ36pef2raZe40ym7Z LkHqUS0g==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1wofMg-00000004rSo-2Iua; Tue, 28 Jul 2026 10:48:50 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 2694430093A; Tue, 28 Jul 2026 12:48:49 +0200 (CEST) Date: Tue, 28 Jul 2026 12:48:49 +0200 From: Peter Zijlstra To: Aaron Tomlin Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, neelx@suse.com, sean@ashe.io, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/debug: Introduce per-CPU debugfs files Message-ID: <20260728104849.GI49951@noisy.programming.kicks-ass.net> References: <20260728020309.6169-1-atomlin@atomlin.com> 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: <20260728020309.6169-1-atomlin@atomlin.com> On Mon, Jul 27, 2026 at 10:03:09PM -0400, Aaron Tomlin wrote: > Currently, accessing scheduler debugging details for a specific CPU > requires reading /sys/kernel/debug/sched/debug, which outputs > information for all online CPUs. This results in redundant output and > parsing overhead on large SMP systems when targeting an individual CPU. > > Add support for per-CPU debug files under: > /sys/kernel/debug/sched/cpu/cpu/debug. Reading > /sys/kernel/debug/sched/cpu/cpu/debug calls print_cpu() specifically > for CPU , exposing CPU-specific runqueue details on demand. You're failing to explain why though. In what situation does the overhead from sched/debug matter one whit? If you're dumping this at frequencies high enough for this to matter, you're doing something terribly wrong.