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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 3625FC433E5 for ; Tue, 28 Jul 2020 10:58:30 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0667A204EA for ; Tue, 28 Jul 2020 10:58:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Hq0F5T7X" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0667A204EA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=xN8UKvuH/Jw2JjwqJ4v2wvRpv8tg5OYOoadY2ZCCla8=; b=Hq0F5T7XZ0Lz1lry/i5a5/VrC 7pV+jMTrPTl/1iMrBVlMSoNQ+SFIWovMEfN6AQgbbBFDcsaJiYieWxQhUFEtNilw/VlzWe3088ixd MyiMiJ5tKoG7Ujb3s3n4SPJz5zD4oll4WCWXZBzCUDf2IdZNjkZm+xFpND87DokSn1Gft+zwsEsRb +NTXNGxCNIPpOH0KWUPk5oGxJuWeIQ2W35UkhkuqzyvBca3b6mhS9W4NsokXYfs57t6PJqeji6q7B Sy9pylkIDE0qBIAkjPDfVGfhFZOYBhXZmUU8kq9sRkGxilwp30cVKT5DsMIZUsYVyBvomFttf/ABr NgLsY401Q==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k0NJT-0004uC-GR; Tue, 28 Jul 2020 10:58:27 +0000 Received: from verein.lst.de ([213.95.11.211]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k0NJQ-0004sw-Ub for linux-nvme@lists.infradead.org; Tue, 28 Jul 2020 10:58:25 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 5FD5668C4E; Tue, 28 Jul 2020 12:58:23 +0200 (CEST) Date: Tue, 28 Jul 2020 12:58:23 +0200 From: Christoph Hellwig To: Sagi Grimberg Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface Message-ID: <20200728105823.GB29763@lst.de> References: <20200727231022.307602-1-sagi@grimberg.me> <20200727231022.307602-2-sagi@grimberg.me> <20200728071859.GA21629@lst.de> <20200728091633.GB1326626@T590> <20200728093326.GC1326626@T590> <44f07df6-3107-3e7f-ee02-7bc43293ee6b@grimberg.me> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <44f07df6-3107-3e7f-ee02-7bc43293ee6b@grimberg.me> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200728_065825_112291_F697336B X-CRM114-Status: GOOD ( 17.82 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , "Paul E. McKenney" , linux-nvme@lists.infradead.org, Ming Lei , linux-block@vger.kernel.org, Chao Leng , Keith Busch , Ming Lin , Christoph Hellwig Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Tue, Jul 28, 2020 at 02:37:15AM -0700, Sagi Grimberg wrote: > >>>>> I like the tagset based interface. But the idea of doing a per-hctx >>>>> allocation and wait doesn't seem very scalable. >>>>> >>>>> Paul, do you have any good idea for an interface that waits on >>>>> multiple srcu heads? As far as I can tell we could just have a single >>>>> global completion and counter, and each call_srcu would just just >>>>> decrement it and then the final one would do the wakeup. It would just >>>>> be great to figure out a way to keep the struct rcu_synchronize and >>>>> counter on stack to avoid an allocation. >>>>> >>>>> But if we can't do with an on-stack object I'd much rather just embedd >>>>> the rcu_head in the hw_ctx. >>>> >>>> I think we can do that, please see the following patch which is against Sagi's V5: >>> >>> I don't think you can send a single rcu_head to multiple call_srcu calls. >> >> OK, then one variant is to put the rcu_head into blk_mq_hw_ctx, and put >> rcu_synchronize into blk_mq_tag_set. > > I can cook up a spin, but I still hate the fact that I have a queue that > ends up quiesced which I didn't want it to... Why do we care so much about the connect_q? Especially if we generalize it into a passthru queue that will absolutely need the quiesce hopefully soon. _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme