From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 9884B2F2E for ; Wed, 16 Jul 2025 13:46:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752673619; cv=none; b=dW+StCB+ZVMNmLNNrQnBoVc4CWAI3MGLNdHzwF7kYVnHMJaFs6ytiaQpkNbMn/3Q4XFeLo329YqEjs9W0Mvc6Cf405acapGDis6S0Jw4pbqRqiH88rqqdiEFA3Zbe6EUnnFqPXTqCXM1a2Jksj9k97GXRUjDcUNddG80KSIUw3Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752673619; c=relaxed/simple; bh=oWqfY4IYFYnZ6rkfKGKz2+ZwKtIQvii/tCymvVf7m4U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=H8YqPtK3EKlW5lQ9N+MkhoRzJ1/X29tp8qO8ldi1LhqICGnRgCoTxJSOsJBsUuija5lbwEG6KXJDKRiZs90Hcy35bnCslZ0dlnl2yhi0bhuVgy0YmRRaHslFWr2JnuvOKQmlIBqm9HF6GEkXfr6T8IW6jS6kjGzbh0a1MwULLPU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ITqEzOdq; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ITqEzOdq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1752673616; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wMSdNvGF0+Gq7PI8vtKmcbLGIURl0DxCtzS+LlFdMfo=; b=ITqEzOdqMC212jJvmC3ecjTvSobfO/ydgqWleM7tOS+jE7J6dJJhC961KNXPkD3QW4nao9 kBjQ3WApqRllPUJitCXQvvgfnxjnAMLs9t/wpLlKo6y1021Br1bfqmSlC/q+6ziWupQUiS Pr7MM5OGZty9mDfaI+3TnKH80X76u0c= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-695-WC3Bwjj9P0K5A8YwX8acZw-1; Wed, 16 Jul 2025 09:46:53 -0400 X-MC-Unique: WC3Bwjj9P0K5A8YwX8acZw-1 X-Mimecast-MFC-AGG-ID: WC3Bwjj9P0K5A8YwX8acZw_1752673612 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9C6D219560B0; Wed, 16 Jul 2025 13:46:51 +0000 (UTC) Received: from pauld.westford.csb (unknown [10.44.32.96]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DB9E61955F16; Wed, 16 Jul 2025 13:46:44 +0000 (UTC) Date: Wed, 16 Jul 2025 09:46:40 -0400 From: Phil Auld To: Shrikanth Hegde Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, 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, clm@meta.com Subject: Re: [PATCH v2 00/12] sched: Address schbench regression Message-ID: <20250716134640.GA20846@pauld.westford.csb> References: <20250702114924.091581796@infradead.org> <132949bc-f901-40e6-a34c-d1d67d03d8b6@linux.ibm.com> <20250707091136.GB1099709@noisy.programming.kicks-ass.net> <49a9e43b-7ca5-4c90-a8b2-c43a84c34aeb@linux.ibm.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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <49a9e43b-7ca5-4c90-a8b2-c43a84c34aeb@linux.ibm.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Hi Peter, On Mon, Jul 07, 2025 at 03:08:08PM +0530 Shrikanth Hegde wrote: > > > On 7/7/25 14:41, Peter Zijlstra wrote: > > On Mon, Jul 07, 2025 at 02:35:38PM +0530, Shrikanth Hegde wrote: > > > > > > > > > On 7/2/25 17:19, Peter Zijlstra wrote: > > > > Hi! > > > > > > > > Previous version: > > > > > > > > https://lkml.kernel.org/r/20250520094538.086709102@infradead.org > > > > > > > > > > > > Changes: > > > > - keep dl_server_stop(), just remove the 'normal' usage of it (juril) > > > > - have the sched_delayed wake list IPIs do select_task_rq() (vingu) > > > > - fixed lockdep splat (dietmar) > > > > - added a few preperatory patches > > > > > > > > > > > > Patches apply on top of tip/master (which includes the disabling of private futex) > > > > and clm's newidle balance patch (which I'm awaiting vingu's ack on). > > > > > > > > Performance is similar to the last version; as tested on my SPR on v6.15 base: > > > > > > > > > > > > > Hi Peter, > > > Gave this a spin on a machine with 5 cores (SMT8) PowerPC system. > > > > > > I see significant regression in schbench. let me know if i have to test different > > > number of threads based on the system size. > > > Will go through the series and will try a bisect meanwhile. > > > > Urgh, those are terrible numbers :/ > > > > What do the caches look like on that setup? Obviously all the 8 SMT > > (is this the supercore that glues two SMT4 things together for backwards > > compat?) share some cache, but is there some shared cache between the > > cores? > > It is a supercore(we call it as bigcore) which glues two SMT4 cores. LLC is > per SMT4 core. So from scheduler perspective system is 10 cores (SMT4) > We've confirmed the issue with schbench on EPYC hardware. It's not limited to PPC systems, although this system may also have interesting caching. We don't see issues with our other tests. --------------- Here are the latency reports from schbench on a single-socket AMD EPYC 9655P server with 96 cores and 192 CPUs. Results for this test: ./schbench/schbench -L -m 4 -t 192 -i 30 -r 30 6.15.0-rc6 baseline threads  wakeup_99_usec  request_99_usec 1        5               3180 16       5               3996 64       3452            14256 128      7112            32960 192      11536           46016 6.15.0-rc6.pz_fixes2 (with 12 part series)) threads  wakeup_99_usec  request_99_usec 1        5               3172 16       5               3844 64       3348            17376 128      21024           100480 192      44224           176384 For 128 and 192 threads, Wakeup and Request latencies increased by a factor of 3x. We're testing now with NO_TTWU_QUEUE_DELAYED and I'll try to report on that when we have results. Cheers, Phil --