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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 6B379C433E0 for ; Tue, 28 Jul 2020 01:51:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 451F620759 for ; Tue, 28 Jul 2020 01:51:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="HRGIKLBJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726340AbgG1BvU (ORCPT ); Mon, 27 Jul 2020 21:51:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59658 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726196AbgG1BvT (ORCPT ); Mon, 27 Jul 2020 21:51:19 -0400 Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 898F4C061794 for ; Mon, 27 Jul 2020 18:51:19 -0700 (PDT) Received: by mail-pl1-x641.google.com with SMTP id d1so9088410plr.8 for ; Mon, 27 Jul 2020 18:51:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=9bjxitCtFHZdGGQj9EyRRYimxiJZ+W4ufp+SOIp69y4=; b=HRGIKLBJvuN7ye9foSLvkE1UJFKxk2DkwyBuwH5xdChA5o0a6gjQZZG+GyS1qicdHn rjN4Q+7ZyE9boM5fm1ekWApZXC8vHjyHQyrp6aXyF7RQ/ZqMwkmqXZ5Epn5FlO7/SUqI eMuC/3BONQ1n02U6OjvXAAY54lSKjxNZjMold2UWn8R3t0sahhwzM5EEpzp8uS3dKrq+ wHgY0b+Mgd2AygqjZSbuAJnR+tdxnESfOjJa4aXabDTHE9TkIB7vv3NDx89Kd4yna17r 69Ijhg+/+RL0vszB6V+ZXbDmxI/YZfKpo3R2Q5mknTP1S6+1Mx0Vs8w38HPC88+K8PXd qpqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=9bjxitCtFHZdGGQj9EyRRYimxiJZ+W4ufp+SOIp69y4=; b=mALFO/cjiBOKo5N58zXufCByXwmZiGOByY3NOYuhKEa0jNqfk18lS8b/7OBe+Lz+VT 2zN/tC9hhuBfcuehcB8r6pvRCx+r0nXFGaxfn4C2MgCscVIPzxbqNLSazzVZCufuE36U MMlkNDvQXHfKEt0WncqgYgOdDBOgtn0ScuJdfYZT/DGdivGfC4gchaqmswitrbZxftTk u+pvLvEMAYL1RwLpqtHiRH4ql6wnJZjr0LcmrWLEy+Qu1mlV5oXTd3SWOB9eTwtvQOJz z8HtBM2jXHytbjxtu4+s2xU/BTgZz8KPuZECHJ8qx/0Zih//9kcQ5Jnal/NhboPBw4sw StPw== X-Gm-Message-State: AOAM530cTD/iM+GytZgaROlKgAsKdkJwPPgHBxnQMloYRZg4c/DNxECW xmveEhXPEHaNMz3tV8VCUMZAzQ== X-Google-Smtp-Source: ABdhPJxOCrD6HZPvqed+snQ0vbyzB4sdQRlakyKKEIn61uHYFCyCDQgk72GEC0pbwcWdJtGFzFoI3A== X-Received: by 2002:a17:902:ead2:: with SMTP id p18mr4992656pld.339.1595901079009; Mon, 27 Jul 2020 18:51:19 -0700 (PDT) Received: from [192.168.1.182] ([66.219.217.173]) by smtp.gmail.com with ESMTPSA id 127sm16616364pgf.5.2020.07.27.18.51.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jul 2020 18:51:18 -0700 (PDT) Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface To: Ming Lei , Sagi Grimberg Cc: linux-nvme@lists.infradead.org, Christoph Hellwig , Keith Busch , linux-block@vger.kernel.org, Ming Lin , Chao Leng References: <20200727231022.307602-1-sagi@grimberg.me> <20200727231022.307602-2-sagi@grimberg.me> <20200728014038.GA1305646@T590> From: Jens Axboe Message-ID: <1d119df0-c3af-2dfa-d569-17109733ac80@kernel.dk> Date: Mon, 27 Jul 2020 19:51:16 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200728014038.GA1305646@T590> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 7/27/20 7:40 PM, Ming Lei wrote: > On Mon, Jul 27, 2020 at 04:10:21PM -0700, Sagi Grimberg wrote: >> drivers that have shared tagsets may need to quiesce potentially a lot >> of request queues that all share a single tagset (e.g. nvme). Add an interface >> to quiesce all the queues on a given tagset. This interface is useful because >> it can speedup the quiesce by doing it in parallel. >> >> For tagsets that have BLK_MQ_F_BLOCKING set, we use call_srcu to all hctxs >> in parallel such that all of them wait for the same rcu elapsed period with >> a per-hctx heap allocated rcu_synchronize. for tagsets that don't have >> BLK_MQ_F_BLOCKING set, we simply call a single synchronize_rcu as this is >> sufficient. >> >> Signed-off-by: Sagi Grimberg >> --- >> block/blk-mq.c | 66 ++++++++++++++++++++++++++++++++++++++++++ >> include/linux/blk-mq.h | 4 +++ >> 2 files changed, 70 insertions(+) >> >> diff --git a/block/blk-mq.c b/block/blk-mq.c >> index abcf590f6238..c37e37354330 100644 >> --- a/block/blk-mq.c >> +++ b/block/blk-mq.c >> @@ -209,6 +209,42 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q) >> } >> EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait); >> >> +static void blk_mq_quiesce_blocking_queue_async(struct request_queue *q) >> +{ >> + struct blk_mq_hw_ctx *hctx; >> + unsigned int i; >> + >> + blk_mq_quiesce_queue_nowait(q); >> + >> + queue_for_each_hw_ctx(q, hctx, i) { >> + WARN_ON_ONCE(!(hctx->flags & BLK_MQ_F_BLOCKING)); >> + hctx->rcu_sync = kmalloc(sizeof(*hctx->rcu_sync), GFP_KERNEL); >> + if (!hctx->rcu_sync) >> + continue; > > This approach of quiesce/unquiesce tagset is good abstraction. > > Just one more thing, please allocate a rcu_sync array because hctx is > supposed to not store scratch stuff. I'd be all for not stuffing this in the hctx, but how would that work? The only thing I can think of that would work reliably is batching the queue+wait into units of N. We could potentially have many thousands of queues, and it could get iffy (and/or unreliable) in terms of allocation size. Looks like rcu_synchronize is 48-bytes on my local install, and it doesn't take a lot of devices at current CPU counts to make an alloc covering all of it huge. Let's say 64 threads, and 32 devices, then we're already at 64*32*48 bytes which is an order 5 allocation. Not friendly, and not going to be reliable when you need it. And if we start batching in reasonable counts, then we're _almost_ back to doing a queue or two at the time... 32 * 48 is 1536 bytes, so we could only do two at the time for single page allocations. -- Jens Axboe