From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CF2566FC5 for ; Mon, 4 Nov 2024 09:28:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730712530; cv=none; b=e1Q468RdHCrr0DKvQGJm/VwsIFSDH+brhU7k8l/UG4jPzTC/c73lE97stTBKSrt/Jwh9m6pLZq9QOriAo3m+uH9R60TyFZzXuc400szFZJwTW7m96JcJAhIqJdxtIkUl6cHOOc1HWKfLFykwHfWq9wu3Vm22cA/dIkrUP7uQPr8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730712530; c=relaxed/simple; bh=/ISMEJMdpURmCFcP3ieimdPjlyxMEpAjqhqp7CNP8Ik=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OnYMM507yvIT8sBMESByLf4RXOEeSrw+cLkwHyVMZ4BnjQ4O6Bnds3amXawRelYnrIkrvQVH2WrGXUkTV6H1nWsSmWw75wsUjr7KxMpcCDul4LihHn6FJaoLNPulnk1lqMIXSCTFtP/UNQs1OQpI1/wp/wLqa3jdFP5jbhr+hmk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AADB0FEC; Mon, 4 Nov 2024 01:29:16 -0800 (PST) Received: from [192.168.178.6] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AFCB53F6A8; Mon, 4 Nov 2024 01:28:44 -0800 (PST) Message-ID: Date: Mon, 4 Nov 2024 10:28:37 +0100 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: [PATCH 17/24] sched/fair: Implement delayed dequeue To: Phil Auld , Peter Zijlstra Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com, wuyun.abel@bytedance.com, youssefesmat@chromium.org, tglx@linutronix.de, efault@gmx.de References: <20240727102732.960974693@infradead.org> <20240727105030.226163742@infradead.org> <20241101124715.GA689589@pauld.westford.csb> From: Dietmar Eggemann Content-Language: en-US In-Reply-To: <20241101124715.GA689589@pauld.westford.csb> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Phil, On 01/11/2024 13:47, Phil Auld wrote: > > Hi Peterm > > On Sat, Jul 27, 2024 at 12:27:49PM +0200 Peter Zijlstra wrote: >> Extend / fix 86bfbb7ce4f6 ("sched/fair: Add lag based placement") by >> noting that lag is fundamentally a temporal measure. It should not be >> carried around indefinitely. >> >> OTOH it should also not be instantly discarded, doing so will allow a >> task to game the system by purposefully (micro) sleeping at the end of >> its time quantum. >> >> Since lag is intimately tied to the virtual time base, a wall-time >> based decay is also insufficient, notably competition is required for >> any of this to make sense. >> >> Instead, delay the dequeue and keep the 'tasks' on the runqueue, >> competing until they are eligible. >> >> Strictly speaking, we only care about keeping them until the 0-lag >> point, but that is a difficult proposition, instead carry them around >> until they get picked again, and dequeue them at that point. > > This one is causing a 10-20% performance hit on our filesystem tests. > > On 6.12-rc5 (so with the latest follow ons) we get: > > with DELAY_DEQUEUE the bandwidth is 510 MB/s > with NO_DELAY_DEQUEUE the bandwidth is 590 MB/s > > The test is fio, something like this: > > taskset -c 1,2,3,4,5,6,7,8 fio --rw randwrite --bs 4k --runtime 1m --fsync 0 --iodepth 32 --direct 1 --ioengine libaio --numjobs 8 --size 30g --nrfiles 1 --loops 1 --name default --randrepeat 1 --time_based --group_reporting --directory /testfs I'm not seeing this on my i7-13700K running tip sched/core (1a6151017ee5 - sched: psi: pass enqueue/dequeue flags to psi callbacks directly (2024-10-26 Johannes Weiner)) (6.12.0-rc4 - based) Using 'taskset 0xaaaaa' avoiding SMT and running only on P-cores. vanilla features: 990MB/s (mean out of 5 runs, σ: 9.38) NO_DELAY_DEQUEUE: 992MB/s (mean out of 5 runs, σ: 10.61) # sudo lshw -class disk -class storage *-nvme description: NVMe device product: GIGABYTE GP-ASM2NE6500GTTD vendor: Phison Electronics Corporation physical id: 0 bus info: pci@0000:01:00.0 logical name: /dev/nvme0 version: EGFM13.2 ... capabilities: nvme pciexpress msix msi pm nvm_express bus_master cap_list configuration: driver=nvme latency=0 nqn=nqn.2014.08.org.nvmexpress:19871987SN215108954872 GIGABYTE GP-ASM2NE6500GTTD state=live resources: irq:16 memory:70800000-70803fff # mount | grep ^/dev/nvme0 /dev/nvme0n1p2 on / type ext4 (rw,relatime,errors=remount-ro) Which disk device you're using? > > In this case it's ext4, but I'm not sure it will be FS specific. > > I should have the machine and setup next week to poke further but I wanted > to mention it now just in case any one has an "aha" moment. > > It seems to only effect these FS loads. Other perf tests are not showing any > issues that I am aware of. [...]