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=-7.6 required=3.0 tests=BAYES_00,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 47B58C433E9 for ; Wed, 27 Jan 2021 17:23:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA8AA60187 for ; Wed, 27 Jan 2021 17:23:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234939AbhA0RWx (ORCPT ); Wed, 27 Jan 2021 12:22:53 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:42157 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233847AbhA0RVR (ORCPT ); Wed, 27 Jan 2021 12:21:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611767991; 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=+zg44t7vpv/TsMxsvWnB8fciySseIuMy7CjnAeu8Zq4=; b=UjW1J1ULRsLcTBqs4/wT2j4RCGCPoXgpF2hC0DxwfcAvbsN/aqrxSuK11TtTTYE5/qHUhb bIoOv9DbwONGa9iiUKENFts+I36sgqzCyUzYCc1IzM1Hi4m3ImNW7HUZ8gpifcb/ZZWXw1 LCq1bfYEePoQjkdYmWltUof9/axWU0c= 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-604-d_68vmW4PhW3YbNf0g7NRA-1; Wed, 27 Jan 2021 12:19:47 -0500 X-MC-Unique: d_68vmW4PhW3YbNf0g7NRA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D3845107ACE4; Wed, 27 Jan 2021 17:19:45 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AD19D10246E0; Wed, 27 Jan 2021 17:19:42 +0000 (UTC) Date: Wed, 27 Jan 2021 12:19:42 -0500 From: Mike Snitzer To: Jeffle Xu Cc: joseph.qi@linux.alibaba.com, dm-devel@redhat.com, linux-block@vger.kernel.org, io-uring@vger.kernel.org Subject: Re: [PATCH v2 0/6] dm: support IO polling for bio-based dm device Message-ID: <20210127171941.GA11530@redhat.com> References: <20210125121340.70459-1-jefflexu@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210125121340.70459-1-jefflexu@linux.alibaba.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Jan 25 2021 at 7:13am -0500, Jeffle Xu wrote: > Since currently we have no simple but efficient way to implement the > bio-based IO polling in the split-bio tracking style, this patch set > turns to the original implementation mechanism that iterates and > polls all underlying hw queues in polling mode. One optimization is > introduced to mitigate the race of one hw queue among multiple polling > instances. > > I'm still open to the split bio tracking mechanism, if there's > reasonable way to implement it. > > > [Performance Test] > The performance is tested by fio (engine=io_uring) 4k randread on > dm-linear device. The dm-linear device is built upon nvme devices, > and every nvme device has one polling hw queue (nvme.poll_queues=1). > > Test Case | IOPS in IRQ mode | IOPS in polling mode | Diff > | (hipri=0) | (hipri=1) | > --------------------------- | ---------------- | -------------------- | ---- > 3 target nvme, num_jobs = 1 | 198k | 276k | ~40% > 3 target nvme, num_jobs = 3 | 608k | 705k | ~16% > 6 target nvme, num_jobs = 6 | 1197k | 1347k | ~13% > 3 target nvme, num_jobs = 6 | 1285k | 1293k | ~0% > > As the number of polling instances (num_jobs) increases, the > performance improvement decreases, though it's still positive > compared to the IRQ mode. I think there is serious room for improvement for DM's implementation; but the block changes for this are all we'd need for DM in the longrun anyway (famous last words). So on a block interface level I'm OK with block patches 1-3. I don't see why patch 5 is needed (said the same in reply to it; but I just saw your reason below..). Anyway, I can pick up DM patches 4 and 6 via linux-dm.git if Jens picks up patches 1-3. Jens, what do you think? > [Optimization] > To mitigate the race when iterating all the underlying hw queues, one > flag is maintained on a per-hw-queue basis. This flag is used to > indicate whether this polling hw queue currently being polled on or > not. Every polling hw queue is exclusive to one polling instance, i.e., > the polling instance will skip this polling hw queue if this hw queue > currently is being polled by another polling instance, and start > polling on the next hw queue. > > This per-hw-queue flag map is currently maintained in dm layer. In > the table load phase, a table describing all underlying polling hw > queues is built and stored in 'struct dm_table'. It is safe when > reloading the mapping table. > > > changes since v1: > - patch 1,2,4 is the same as v1 and have already been reviewed > - patch 3 is refactored a bit on the basis of suggestions from > Mike Snitzer. > - patch 5 is newly added and introduces one new queue flag > representing if the queue is capable of IO polling. This mainly > simplifies the logic in queue_poll_store(). Ah OK, don't see why we want to eat a queue flag for that though! > - patch 6 implements the core mechanism supporting IO polling. > The sanity check checking if the dm device supports IO polling is > also folded into this patch, and the queue flag will be cleared if > it doesn't support, in case of table reloading. Thanks, Mike