From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 95CAE399000; Fri, 18 Sep 2026 07:08:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789715325; cv=none; b=lxt6/v1JNFZpu9GirATi3bCCovltAGM3kxxSDwIYlEZ5EnQ1waolka/LdHRQ0/HxKDEkbPKIYp0paK2lAf7A8WshkraqcAjG9p6SH9qHm1UwfBML6XySr6Agk6OV9enGnQ4Zw8fJoybDKjxhq2/YO/nbwpZ7Ulz1IdfMrk9Wbvc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789715325; c=relaxed/simple; bh=X2eUEqkirypJ4tNw27O3rKlkmu6pev06r3OHZ0yobOM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eidJsPbsmfHQEu2mawFpDfaddX1xNO2CM8y5aIuZce38s3bG6X2dKe2ZDY++u0oY4LWs5MT2w9AQ5c37tta3ngF51ltWb5ElNi0s4eSyEJFyp9zp6CsKd7K4NOnCh6Nrj8iBjD+4lgHQS4Mp1yw8oLWX7LKQrGb4+6TqKKbAL4c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Awku+uV8; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Awku+uV8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3E9E1F000FF; Fri, 18 Sep 2026 07:08:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789715324; bh=WCL4dePjhuTX+CGE5tvS1dbBZl4n5dA5dLQyhLK3zT8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Awku+uV8pxJg2xgDDCtl5/l75ccjfY+SVllzMvrfHWYiQtLqHtEiXmIY92vIOOLqA sw+p8lDtPlpSpOCo6STc40T4j4ymvTQ8miSZNMQeBBBm5EA7WucrIMgYeH8wuuM/DG +BfgFttLkbWWOmkrZgLyIIMf/YZnzRxDgoxY8eXn76fo0NBew4JbrSvc+cRNfaFiAl QkEWcPh0v2r3CBUEUYOst7UeoaOyYdLc4pb1uRmVVT2l0puoiHyRr+BB00fdwvDOte zMTrahakOeCUcuHDF8D2CjLZFngzAzI+3HVShn15UKErn1OlTsiT38Xn3cVrzIAtYv 8z5PR0qB8xmPA== Message-ID: <8705aa4f-5e02-45e7-ad45-0baa982a8c02@kernel.org> Date: Fri, 18 Sep 2026 09:08:37 +0200 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: [SLUB] nfs_page cmpxchg_double_fail and perf lock perturbation on dual-socket NFS/RDMA Content-Language: en-US To: Tim Menninger , Harry Yoo Cc: linux-mm@kvack.org, Chuck Lever , linux-nfs@vger.kernel.org, Jon Curley , Eric Badger , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260917162533.600472-1-tmenninger@everpuredata.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/17/26 18:25, Tim Menninger wrote: > It reproduces with slab_nomerge. > > I booted the same kernel with: > > $ cat /proc/cmdline > ... slab_nomerge ... > > Uninstrumented throughput remains in the high-45 to low-46 GB/s > range, as before. During perf lock it was around 30 GB/s in these > runs, versus roughly 25 GB/s previously. > > The dominant lock measurements are essentially unchanged: > > default slab_nomerge > unpinned/node0 > contentions 4,782,839 4,858,759 > total wait 14.39 min 14.26 min > average wait 180.47 us 176.13 us > > node0/node0 > contentions 4,582,012 4,686,729 > total wait 14.13 min 14.34 min > average wait 185.05 us 183.53 us > > unpinned/balanced > contentions 4,572,196 4,544,677 > total wait 12.81 min 12.56 min > average wait 168.14 us 165.84 us > > The uninstrumented cmpxchg_double_fail deltas were: > > default slab_nomerge > unpinned/node0 7,471 8,892 > node0/node0 713 457 > unpinned/balanced 1,503 1,504 > > The CPU-utilization change while perf lock is active also remains. > System-wide %idle for uninstrumented/instrumented windows was: > > default slab_nomerge > uninstr. instr. uninstr. instr. > unpinned/node0 31.46% 3.60% 23.02% 2.15% > node0/node0 84.26% 12.07% 84.62% 11.85% > unpinned/balanced 66.86% 14.83% 66.58% 14.78% I believe the weirdest part in the original report was how slub stat counters such as free_fastpath etc got order of magnitude higher with instrumented vs non-instrumented. Did any of that change with slab_nomerge? > Thanks, > Tim