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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76B8AC433EF for ; Thu, 30 Sep 2021 09:02:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5399361882 for ; Thu, 30 Sep 2021 09:02:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348727AbhI3JE3 (ORCPT ); Thu, 30 Sep 2021 05:04:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43308 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237229AbhI3JE3 (ORCPT ); Thu, 30 Sep 2021 05:04:29 -0400 Received: from mail-wr1-x434.google.com (mail-wr1-x434.google.com [IPv6:2a00:1450:4864:20::434]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8CB0C06176A for ; Thu, 30 Sep 2021 02:02:46 -0700 (PDT) Received: by mail-wr1-x434.google.com with SMTP id i23so8847987wrb.2 for ; Thu, 30 Sep 2021 02:02:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=to:cc:references:from:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=cDgtvPtGqhn9GDtQPDQD7GjBBk8pv0exfjRSSpHvoo8=; b=CQsmCnlUxRsiR1HhvmC213ZmFX+INhMKgKCkWbwVaHh/OcW2figJEYgz3TctTWU3Gw H/5h8CfneB88mgn7l7rKnie0XBBo2ZnUxT7hDHDwStjqkbc7YTsexvTojslef9S0eXCp X1VrDfy+CupzjBmvN+u6FKFVg1bNRqeleq/0NyUWaaEOxeND0sK3k8/gBXXhzM/HkpuX DY7CrFtUMmnjfZJvNlIz2WCeslXKInQ966Yu1yHwsCfgu4K9pntbnP9E3k5rwzPkXOb1 HnavU/ZkhCSm6fz3WTVmeoAei9rQD1NE+Xtr6gRm04yAbjdotyuoht0+0Accdhoao98E Qkrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:to:cc:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=cDgtvPtGqhn9GDtQPDQD7GjBBk8pv0exfjRSSpHvoo8=; b=JrSL8VMlmXCkRMbDVsjSnR8AMIyiwJk7k383+DQCOIWn5bCcJjrEUL9+IsZkE+UVTZ x9hihOU0Cx1oXf1OZH6Le5XEILzZCPpBHhnMU8q7sZW7ypZKEQf/Cs8aq1KPkSDr5Mv8 rRECFqSEsSrWogg5kiOkIdl+kD8vP88kH1T7EJcrVTn+WSme6k3JcZjAWGnxYNfRrteK EAu1S4Cwj38/+TSu+auzV9ZcnwUcFD5ENVeh6FrWFG2/QulNaIbWHeNsP+ffl9ww0/mf ATavZk9QjWvw1A3HJvC2mTBigXvaf5XKFBPTr7bTELJIzMgSlbDCefPs7xQHw4EkrWOG xoHg== X-Gm-Message-State: AOAM533tzW7uUqLobHCajLylrUKRJzyS9gBAZ5IXBayoFqkUdigDAn1z TgXFGW2KMm/pukOH3p11aEATw4m8CP0= X-Google-Smtp-Source: ABdhPJzg9HbbiOK2Qf09jV3F3bcFj5aAFDuBidzI7cvWMuPrLOrjLsnNTDjZRFwhcYjyNc//bNMq5w== X-Received: by 2002:adf:fb50:: with SMTP id c16mr4868008wrs.120.1632992565461; Thu, 30 Sep 2021 02:02:45 -0700 (PDT) Received: from [192.168.8.197] ([85.255.233.40]) by smtp.gmail.com with ESMTPSA id j7sm2796102wrr.27.2021.09.30.02.02.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Sep 2021 02:02:45 -0700 (PDT) To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210927061721.180806-1-haoxu@linux.alibaba.com> <20210927061721.180806-4-haoxu@linux.alibaba.com> <5c1ffe9e-23e7-3b50-b48c-6a87c2c7d1ba@linux.alibaba.com> From: Pavel Begunkov Subject: Re: [PATCH 3/8] io_uring: add a limited tw list for irq completion work Message-ID: Date: Thu, 30 Sep 2021 10:02:07 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <5c1ffe9e-23e7-3b50-b48c-6a87c2c7d1ba@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/29/21 12:38 PM, Hao Xu wrote: > 在 2021/9/28 下午7:29, Pavel Begunkov 写道: [...] >>>   @@ -2132,12 +2136,16 @@ static void tctx_task_work(struct callback_head *cb) >>>       while (1) { >>>           struct io_wq_work_node *node; >>>   -        if (!tctx->task_list.first && locked) >>> +        if (!tctx->prior_task_list.first && >>> +            !tctx->task_list.first && locked) >>>               io_submit_flush_completions(ctx); >>>             spin_lock_irq(&tctx->task_lock); >>> -        node = tctx->task_list.first; >>> +        wq_list_merge(&tctx->prior_task_list, &tctx->task_list); >>> +        node = tctx->prior_task_list.first; >> >> I find all this accounting expensive, sure I'll see it for my BPF tests. > May I ask how do you evaluate the overhead with BPF here? It's a custom branch and apparently would need some thinking on how to apply your stuff on top, because of yet another list in [1]. In short, the case in mind spins inside of tctx_task_work() doing one request at a time. I think would be easier if I try it out myself. [1] https://github.com/isilence/linux/commit/d6285a9817eb26aa52ad54a79584512d7efa82fd >> >> How about >> 1) remove MAX_EMERGENCY_TW_RATIO and all the counters, >> prior_nr and others. >> >> 2) rely solely on list merging >> >> So, when it enters an iteration of the loop it finds a set of requests >> to run, it first executes all priority ones of that set and then the >> rest (just by the fact that you merged the lists and execute all from >> them). >> >> It solves the problem of total starvation of non-prio requests, e.g. >> if new completions coming as fast as you complete previous ones. One >> downside is that prio requests coming while we execute a previous >> batch will be executed only after a previous batch of non-prio >> requests, I don't think it's much of a problem but interesting to >> see numbers. > hmm, this probably doesn't solve the starvation, since there may be > a number of priority TWs ahead of non-prio TWs in one iteration, in the > case of submitting many sqes in one io_submit_sqes. That's why I keep > just 1/3 priority TWs there. I don't think it's a problem, they should be fast enough and we have a forward progress guarantees for non-prio. IMHO that should be enough. >> >> >>>           INIT_WQ_LIST(&tctx->task_list); >>> +        INIT_WQ_LIST(&tctx->prior_task_list); >>> +        tctx->nr = tctx->prior_nr = 0; >>>           if (!node) >>>               tctx->task_running = false; >>>           spin_unlock_irq(&tctx->task_lock); >>> @@ -2166,7 +2174,7 @@ static void tctx_task_work(struct callback_head *cb) >>>       ctx_flush_and_put(ctx, &locked); >>>   } >>>   -static void io_req_task_work_add(struct io_kiocb *req) >>> +static void io_req_task_work_add(struct io_kiocb *req, bool emergency) >> >> It think "priority" instead of "emergency" will be more accurate >> >>>   { >>>       struct task_struct *tsk = req->task; >>>       struct io_uring_task *tctx = tsk->io_uring; >>> @@ -2178,7 +2186,13 @@ static void io_req_task_work_add(struct io_kiocb *req) >>>       WARN_ON_ONCE(!tctx); >>>         spin_lock_irqsave(&tctx->task_lock, flags); >>> -    wq_list_add_tail(&req->io_task_work.node, &tctx->task_list); >>> +    if (emergency && tctx->prior_nr * MAX_EMERGENCY_TW_RATIO < tctx->nr) { >>> +        wq_list_add_tail(&req->io_task_work.node, &tctx->prior_task_list); >>> +        tctx->prior_nr++; >>> +    } else { >>> +        wq_list_add_tail(&req->io_task_work.node, &tctx->task_list); >>> +    } >>> +    tctx->nr++; >>>       running = tctx->task_running; >>>       if (!running) >>>           tctx->task_running = true; >> >> >> > -- Pavel Begunkov