From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0346CC433DF for ; Wed, 24 Jun 2020 05:22:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE9DB2072E for ; Wed, 24 Jun 2020 05:22:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YciUBurx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388883AbgFXFWU (ORCPT ); Wed, 24 Jun 2020 01:22:20 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:60260 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727957AbgFXFWU (ORCPT ); Wed, 24 Jun 2020 01:22:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592976138; 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: in-reply-to:in-reply-to:references:references; bh=SXtCMYzuSyQmAhIf24ZY39KZ53JUuAnzaU1mt7pqaeM=; b=YciUBurxt5IjO71XDMme47TNohjCUamJdh4uxnbYQF4IgHMajTtEPL6jiLLK5n+weZD0D3 Cl6Cksg2U1rlHharGYjV31kGlOKQ9bTMWF5BioJi1bxYQJRH5FrjoDi3hNEVyPhldIm3ES R+ARMgJPS365yDUrr9jS5yQx4QgDOXg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-168-iGFLzro-NT-trKNSaDgH8Q-1; Wed, 24 Jun 2020 01:22:14 -0400 X-MC-Unique: iGFLzro-NT-trKNSaDgH8Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1A2FC8015F0; Wed, 24 Jun 2020 05:22:13 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 292FF7168B; Wed, 24 Jun 2020 05:22:10 +0000 (UTC) Date: Wed, 24 Jun 2020 01:22:09 -0400 From: Mike Snitzer To: Damien Le Moal Cc: Ignat Korchagin , "kernel-team@cloudflare.com" , "dm-crypt@saout.de" , "linux-kernel@vger.kernel.org" , "dm-devel@redhat.com" , Mikulas Patocka , "agk@redhat.com" Subject: Re: [RFC PATCH 0/1] dm-crypt excessive overhead Message-ID: <20200624052209.GB23205@redhat.com> References: <20200619164132.1648-1-ignat@cloudflare.com> <20200619165548.GA24779@redhat.com> <20200623150118.GA19657@redhat.com> <20200623152235.GB19657@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 24 2020 at 12:54am -0400, Damien Le Moal wrote: > On 2020/06/24 0:23, Mike Snitzer wrote: > > On Tue, Jun 23 2020 at 11:07am -0400, > > Ignat Korchagin wrote: > > > >> Do you think it may be better to break it in two flags: one for read > >> path and one for write? So, depending on the needs and workflow these > >> could be enabled independently? > > > > If there is a need to split, then sure. But I think Damien had a hard > > requirement that writes had to be inlined but that reads didn't _need_ > > to be for his dm-zoned usecase. Damien may not yet have assessed the > > performance implications, of not have reads inlined, as much as you > > have. > > We did do performance testing :) > The results are mixed and performance differences between inline vs workqueues > depend on the workload (IO size, IO queue depth and number of drives being used > mostly). In many cases, inlining everything does really improve performance as > Ignat reported. > > In our testing, we used hard drives and so focused mostly on throughput rather > than command latency. The added workqueue context switch overhead and crypto > work latency compared to typical HDD IO times is small, and significant only if > the backend storage as short IO times. > > In the case of HDDs, especially for large IO sizes, inlining crypto work does > not shine as it prevents an efficient use of CPU resources. This is especially > true with reads on a large system with many drives connected to a single HBA: > the softirq context decryption work does not lend itself well to using other > CPUs that did not receive the HBA IRQ signaling command completions. The test > results clearly show much higher throughputs using dm-crypt as is. > > On the other hand, inlining crypto work significantly improves workloads of > small random IOs, even for a large number of disks: removing the overhead of > context switches allows faster completions, allowing sending more requests to > the drives more quickly, keeping them busy. > > For SMR, the inlining of write requests is *mandatory* to preserve the issuer > write sequence, but encryption work being done in the issuer context (writes to > SMR drives can only be O_DIRECT writes), efficient CPU resource usage can be > achieved by simply using multiple writer thread/processes, working on different > zones of different disks. This is a very reasonable model for SMR as writes into > a single zone have to be done under mutual exclusion to ensure sequentiality. > > For reads, SMR drives are essentially exactly the same as regular disks, so > as-is or inline are both OK. Based on our performance results, allowing the user > to have the choice of inlining or not reads based on the target workload would > be great. > > Of note is that zone append writes (emulated in SCSI, native with NVMe) are not > subject to the sequential write constraint, so they can also be executed either > inline or asynchronously. > > > So let's see how Damien's work goes and if he trully doesn't need/want > > reads to be inlined then 2 flags can be created. > > For SMR, I do not need inline reads, but I do want the user to have the > possibility of using this setup as that can provide better performance for some > workloads. I think that splitting the inline flag in 2 is exactly what we want: > > 1) For SMR, the write-inline flag can be automatically turned on when the target > device is created if the backend device used is a host-managed zoned drive (scsi > or NVMe ZNS). For reads, it would be the user choice, based on the target workload. > 2) For regular block devices, write-inline only, read-inline only or both would > be the user choice, to optimize for their target workload. > > With the split into 2 flags, my SMR support patch becomes very simple. OK, thanks for all the context. Was a fun read ;) SO let's run with splitting into 2 flags. Ignat would you be up to tweaking your patch to provide that and post a v2? An added bonus would be to consolidate your 0/1 and 1/1 patch headers, and add in the additional answers you provided in this thread to help others understand the patch (mainly some more detail about why tasklet is used). Thanks, Mike