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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 94A09CA9EAF for ; Mon, 21 Oct 2019 11:50:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 624A420659 for ; Mon, 21 Oct 2019 11:50:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727685AbfJULuD (ORCPT ); Mon, 21 Oct 2019 07:50:03 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:50072 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726767AbfJULuC (ORCPT ); Mon, 21 Oct 2019 07:50:02 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 0C2C893130F6F3E865A0; Mon, 21 Oct 2019 19:50:00 +0800 (CST) Received: from [127.0.0.1] (10.202.227.179) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.439.0; Mon, 21 Oct 2019 19:49:58 +0800 Subject: Re: [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug To: Ming Lei References: <20191014015043.25029-1-ming.lei@redhat.com> <20191016120729.GB5515@ming.t460p> <9dbc14ab-65cd-f7ac-384c-2dbe03575ee7@huawei.com> <55a84ea3-647d-0a76-596c-c6c6b2fc1b75@huawei.com> <20191020101404.GA5103@ming.t460p> <10aac76a-26bb-bcda-c6ea-b39ca66d6740@huawei.com> <20191021093448.GA22635@ming.t460p> <9e6e86a5-7247-4648-9df9-61f81d2df413@huawei.com> <20191021102401.GB22635@ming.t460p> CC: Jens Axboe , , "Bart Van Assche" , Hannes Reinecke , "Christoph Hellwig" , Thomas Gleixner , Keith Busch From: John Garry Message-ID: Date: Mon, 21 Oct 2019 12:49:53 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20191021102401.GB22635@ming.t460p> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.179] X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org >>> >> >> Yes, we share tags among all queues, but we generate the tag - known as IPTT >> - in the LLDD now, as we can no longer use the request tag (as it is not >> unique per all queues): >> >> https://github.com/hisilicon/kernel-dev/commit/087b95af374be6965583c1673032fb33bc8127e8#diff-f5d8fff19bc539a7387af5230d4e5771R188 >> >> As I said, the branch is messy and I did have to fix 087b95af374. > > Firstly this way may waste lots of memory, especially the queue depth is > big, such as, hisilicon V3's queue depth is 4096. > > Secondly, you have to deal with queue busy efficiently and correctly, > for example, your real hw tags(IPTT) can be used up easily, and how > will you handle these dispatched request? I have not seen scenario of exhausted IPTT. And IPTT count is same as SCSI host.can_queue, so SCSI midlayer should ensure that this does not occur. > > Finally, you have to evaluate the performance effect, this is highly > related with how to deal with out-of-IPTT. Some figures from our previous testing: Managed interrupt without exposing multiple queues: 3M IOPs Managed interrupt with exposing multiple queues: 2.6M IOPs No managed interrupts: 500K IOPs. Now my problem is that I hear some people are relying on the 3M performance, even though it is experimental and unsafe. I need to follow up on this. I really don't want to keep that code. > > I'd suggest you to fix the stuff and post them out for review. OK, I'll also check on adding that WARN you provided. Thanks again, John > > Thanks, > Ming > > > . >