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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7EFDC433F5 for ; Tue, 29 Mar 2022 13:48:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231233AbiC2NuH (ORCPT ); Tue, 29 Mar 2022 09:50:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39554 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237495AbiC2NuG (ORCPT ); Tue, 29 Mar 2022 09:50:06 -0400 Received: from mail-pj1-x1033.google.com (mail-pj1-x1033.google.com [IPv6:2607:f8b0:4864:20::1033]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E31D5DF62 for ; Tue, 29 Mar 2022 06:48:22 -0700 (PDT) Received: by mail-pj1-x1033.google.com with SMTP id bx5so17483955pjb.3 for ; Tue, 29 Mar 2022 06:48:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=mXJzlYVD+DjRpLpJGhDOsMh/Zm7JLhIX2UQq7rw4yPE=; b=eqnECCcd+u9x8y9FzmZJ8pwNzk0Dw/CMSrWV87z+douBIJPnoQQhWmANKoW73csgzW +XH7kBLWddafq/9R/1eUGNzpE13I50PPr/VVQpHJfMAsLU8yLH+6RkkqsbF1fa6KS5pp IdVvUeEOm3YVPomgJh/bzpyW1cd0MGo8Fucu3RjR/pLUhVdNwsp3l+vjOvu2PCK2zTzL MMvkF1afnUal9d85xg4yl8jwWZWhljVywakg8FZggNwBkKFtvRmdEa8jJvmRbLpZob0i lxmy39nQ2O51j3QVed8MwawJpDJ/XJ3xvmPPPSRe6I3nzdS6h7bcyj3qO1CRtTuCaSHw g4lQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=mXJzlYVD+DjRpLpJGhDOsMh/Zm7JLhIX2UQq7rw4yPE=; b=fBTwD8lVJhXFQp7yeV0PX1UOjY9UQ2cxIvuSSwsQDs3ndvDyl/5hKsoqyms7nHf0bQ 5iM5yfNv2MhbSnADBYHQcAoY8wNSzzOisYd0aSNhQddrn38czGABnEQItHNw0kkjJKHL iW16mUreeQKSjA98ziuEF7nkuw6qUAoiMjq3pCRZSD3+kDjrLX4tGVMLzZ/E0rb3HQrz 91mhS86ylatmoafjOzvva0wvuMJufmg7CAGDSciIoMGnXas9zVUZtdYuBZWv1BSfaLnd Q1yJAyY+5qC9E0dbN9mB0kEiSKZMmSpr1c/L08INEqMqTnpgVuzzlxLdBZaszl+Qr97n Uk2g== X-Gm-Message-State: AOAM532ATLVoVyoCeAnuAeIs2QzEBMPZpmrC2pd921oj0rWsW15IwTPK dHjobikYzrJ4Masoh+zuaWtMelE6DN86KQ== X-Google-Smtp-Source: ABdhPJzb9vb3N4M/AhAbUFwMLp8Nt874tOSGcAmrfKNTGmabDmT0KRKuC3Mh18ATB0qgNXzoAzbz9g== X-Received: by 2002:a17:90b:4b89:b0:1c8:105a:2262 with SMTP id lr9-20020a17090b4b8900b001c8105a2262mr4663568pjb.225.1648561702321; Tue, 29 Mar 2022 06:48:22 -0700 (PDT) Received: from localhost.localdomain ([114.200.4.15]) by smtp.gmail.com with ESMTPSA id gk13-20020a17090b118d00b001c6b2472576sm3101842pjb.19.2022.03.29.06.48.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Mar 2022 06:48:21 -0700 (PDT) Date: Tue, 29 Mar 2022 22:48:16 +0900 From: Suwan Kim To: Stefan Hajnoczi Cc: mst@redhat.com, jasowang@redhat.com, pbonzini@redhat.com, mgurtovoy@nvidia.com, virtualization@lists.linux-foundation.org, linux-block@vger.kernel.org Subject: Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs() Message-ID: References: <20220324140450.33148-1-suwan.kim027@gmail.com> <20220324140450.33148-3-suwan.kim027@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Mar 29, 2022 at 09:45:29AM +0100, Stefan Hajnoczi wrote: > On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote: > > On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote: > > > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote: > > > > +static void virtio_queue_rqs(struct request **rqlist) > > > > +{ > > > > + struct request *req, *next, *prev = NULL; > > > > + struct request *requeue_list = NULL; > > > > + > > > > + rq_list_for_each_safe(rqlist, req, next) { > > > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data; > > > > + unsigned long flags; > > > > + bool kick; > > > > + > > > > + if (!virtblk_prep_rq_batch(vq, req)) { > > > > + rq_list_move(rqlist, &requeue_list, req, prev); > > > > + req = prev; > > > > + > > > > + if (!req) > > > > + continue; > > > > + } > > > > + > > > > + if (!next || req->mq_hctx != next->mq_hctx) { > > > > + spin_lock_irqsave(&vq->lock, flags); > > > > > > Did you try calling virtblk_add_req() here to avoid acquiring and > > > releasing the lock multiple times? In other words, do virtblk_prep_rq() > > > but wait until we get here to do virtblk_add_req(). > > > > > > I don't know if it has any measurable effect on performance or maybe the > > > code would become too complex, but I noticed that we're not fully > > > exploiting batching. > > > > I tried as you said. I called virtlblk_add_req() and added requests > > of rqlist to virtqueue in this if statement with holding the lock > > only once. > > > > I attach the code at the end of this mail. > > Please refer the code. > > > > But I didn't see improvement. It showed slightly worse performance > > than the current patch. > > Okay, thanks for trying it! > > > > > + kick = virtqueue_kick_prepare(vq->vq); > > > > + spin_unlock_irqrestore(&vq->lock, flags); > > > > + if (kick) > > > > + virtqueue_notify(vq->vq); > > > > + > > > > + req->rq_next = NULL; > > > > Did you ask this part? > > > > > > + *rqlist = next; > > > > + prev = NULL; > > > > + } else > > > > + prev = req; > > > > > > What guarantees that req is still alive after we called > > > virtblk_add_req()? The device may have seen it and completed it already > > > by the time we get here. > > > > Isn't request completed after the kick? > > > > If you asked about "req->rq_next = NULL", > > I think it should be placed before > > "kick = virtqueue_kick_prepare(vq->vq);" > > > > ----------- > > req->rq_next = NULL; > > kick = virtqueue_kick_prepare(vq->vq); > > spin_unlock_irqrestore(&vq->lock, flags); > > if (kick) > > virtqueue_notify(vq->vq); > > ----------- > > No, virtqueue_add_sgs() exposes vring descriptors to the device. The > device may process immediately. In other words, VIRTIO devices may poll > the vring instead of waiting for virtqueue_notify(). There is no > guarantee that the request is alive until virtqueue_notify() is called. > > The code has to handle the case where the request is completed during > virtqueue_add_sgs(). Thanks for the explanation. We should not use req again after virtblk_add_req(). I understand... Then, as you commented in previous mail, is it ok that we do virtblk_add_req() in "if (!next || req->mq_hctx != next->mq_hctx)" statement to avoid use req again after virtblk_add_req() as below code? In this code, It adds reqs to virtqueue in batch just before virtqueue_notify(), and it doesn't use req again after calling virtblk_add_req(). If it is fine, I will try it again. This code is slightly different from the code I sent in previous mail. --- static void virtio_queue_rqs(struct request **rqlist) ... rq_list_for_each_safe(rqlist, req, next) { ... if (!next || req->mq_hctx != next->mq_hctx) { // Cut the list at current req req->rq_next = NULL; // Add req list to virtqueue in batch with holding lock once kick = virtblk_add_req_batch(vq, rqlist, &requeue_list); if (kick) virtqueue_notify(vq->vq); // setup new req list. Don't use previous req again. *rqlist = next; prev = NULL; ... --- Regards, Suwan Kim