From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f197.google.com (mail-io0-f197.google.com [209.85.223.197]) by kanga.kvack.org (Postfix) with ESMTP id 29A5B6B0038 for ; Thu, 4 May 2017 17:27:41 -0400 (EDT) Received: by mail-io0-f197.google.com with SMTP id x86so30194240ioe.5 for ; Thu, 04 May 2017 14:27:41 -0700 (PDT) Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com. [67.231.145.42]) by mx.google.com with ESMTPS id k16si28859783ioo.132.2017.05.04.14.27.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 04 May 2017 14:27:40 -0700 (PDT) Date: Thu, 4 May 2017 14:27:26 -0700 From: Shaohua Li Subject: Re: [PATCH] swap: add block io poll in swapin path Message-ID: <20170504212725.GA26681@MacBook-Pro.dhcp.thefacebook.com> References: <7dd0349ba5d321af557d7a09e08610f2486ea29e.1493930299.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Jens Axboe Cc: linux-mm@kvack.org, Andrew Morton , Kernel-team@fb.com, Tim Chen , Huang Ying On Thu, May 04, 2017 at 02:53:59PM -0600, Jens Axboe wrote: > On 05/04/2017 02:42 PM, Shaohua Li wrote: > > For fast flash disk, async IO could introduce overhead because of > > context switch. block-mq now supports IO poll, which improves > > performance and latency a lot. swapin is a good place to use this > > technique, because the task is waitting for the swapin page to continue > > execution. > > Nitfy! > > > In my virtual machine, directly read 4k data from a NVMe with iopoll is > > about 60% better than that without poll. With iopoll support in swapin > > patch, my microbenchmark (a task does random memory write) is about 10% > > ~ 25% faster. CPU utilization increases a lot though, 2x and even 3x CPU > > utilization. This will depend on disk speed though. While iopoll in > > swapin isn't intended for all usage cases, it's a win for latency > > sensistive workloads with high speed swap disk. block layer has knob to > > control poll in runtime. If poll isn't enabled in block layer, there > > should be no noticeable change in swapin. > > Did you try with hybrid polling enabled? We should be able to achieve > most of the latency win at much less CPU cost with that. Hybrid poll is much slower than classic in my test, I tried different settings. maybe because this is a vm though. Thanks, Shaohua -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org