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 59471C433FE for ; Tue, 5 Apr 2022 11:48:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244874AbiDELuE (ORCPT ); Tue, 5 Apr 2022 07:50:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351617AbiDELEv (ORCPT ); Tue, 5 Apr 2022 07:04:51 -0400 Received: from mail-pj1-x1032.google.com (mail-pj1-x1032.google.com [IPv6:2607:f8b0:4864:20::1032]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B81FE43AD for ; Tue, 5 Apr 2022 03:30:37 -0700 (PDT) Received: by mail-pj1-x1032.google.com with SMTP id fu5so5729669pjb.1 for ; Tue, 05 Apr 2022 03:30:37 -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=usRiKAzT3qrPf6y3eLeMLx4S2c8/Cp+tKib9umJYw4g=; b=HAX/4vUur7dDmKA87YjTzm62mZb8y1JLy4WTpJUzkJTP9mEkeALma99rhX8AHsrS6Q aq2FfY30Bkg1P/znx72dakUK0CQQWsmEB94+TN83VNf0NT5hcbw1HfFnoXpU5dc4I3xR 9QeeM+epWjKGBph11iWIwKK1msw5nty6dp4YFWh4nh6FWUu9/Kphg3MVpQOn2C/trOWc YS2XYBmTBPE7hS//SPqxGu2woFsKzq56+pVIPns+pYGf0VE3OPN94JrJCRcJ4CRU4dbu EIyFuB1x+D3vhZCwAVxuZebtceBMOjkF66LYZLHptxWDEI+5lgwjqRs4fe7S2cJEBeQS GoAw== 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=usRiKAzT3qrPf6y3eLeMLx4S2c8/Cp+tKib9umJYw4g=; b=wHD+kyPiT5CWMiBmtuEOyQbhhPR6bbO5dyCh1jPyl8L6u5wdxlOk55v+GHXnf6FtzB gU0JpgoLF4ki2Foh8+1uRmnUUfsyHxFzaShWmo/vJn8H4bU57xUcy+gHdAyCvPjq/gka s368wTqgaxj06CrTnisFwsd1ct0mOsBeLIE+f8e4zIl/FPnq50jTjsl1mcE3BS+26Jcl By/zj0IF53NZHonq6RAWud/EIEBji+GXX5cJ42O1g0uhXj/zOFCbdfn6ySTb60AmZ/kI qHuySoV1MQBKmJUP9+U+OBtOd0cVHCXgmrXXH9UcqutKX7nhguWUZMNWw7BfJIJ6Rp6i 8nqQ== X-Gm-Message-State: AOAM532KylAYxafe8nQyzZVLUv9OZu5GyB6oTh142nRPSjdufqIxKwlH ueI+y+p12+gwZ/SwJ7odRsE= X-Google-Smtp-Source: ABdhPJzpsBGipfDj5+LPDmtCMQBqrzgOO9On2DXDgbT+QR4oIqoF0SJq0XBTxjuWuVZuw+wb7IUBpw== X-Received: by 2002:a17:90b:1809:b0:1c7:28fb:bdd0 with SMTP id lw9-20020a17090b180900b001c728fbbdd0mr3182699pjb.231.1649154636931; Tue, 05 Apr 2022 03:30:36 -0700 (PDT) Received: from localhost.localdomain ([114.200.4.15]) by smtp.gmail.com with ESMTPSA id oj16-20020a17090b4d9000b001c709bca712sm2201801pjb.29.2022.04.05.03.30.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Apr 2022 03:30:36 -0700 (PDT) Date: Tue, 5 Apr 2022 19:30:30 +0900 From: Suwan Kim To: Christoph Hellwig Cc: mst@redhat.com, jasowang@redhat.com, stefanha@redhat.com, pbonzini@redhat.com, mgurtovoy@nvidia.com, dongli.zhang@oracle.com, virtualization@lists.linux-foundation.org, linux-block@vger.kernel.org Subject: Re: [PATCH v4 1/2] virtio-blk: support polling I/O Message-ID: References: <20220405053122.77626-1-suwan.kim027@gmail.com> <20220405053122.77626-2-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, Apr 05, 2022 at 01:51:40AM -0700, Christoph Hellwig wrote: > On Tue, Apr 05, 2022 at 02:31:21PM +0900, Suwan Kim wrote: > > This patch supports polling I/O via virtio-blk driver. Polling > > feature is enabled by module parameter "num_poll_queues" and it > > sets dedicated polling queues for virtio-blk. This patch improves > > the polling I/O throughput and latency. > > > > The virtio-blk driver doesn't not have a poll function and a poll > > queue and it has been operating in interrupt driven method even if > > the polling function is called in the upper layer. > > > > virtio-blk polling is implemented upon 'batched completion' of block > > layer. virtblk_poll() queues completed request to io_comp_batch->req_list > > and later, virtblk_complete_batch() calls unmap function and ends > > the requests in batch. > > > > virtio-blk reads the number of poll queues from module parameter > > "num_poll_queues". If VM sets queue parameter as below, > > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter]) > > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)] > > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default > > queues, the poll queues have no callback function. > > > > Regarding HW-SW queue mapping, the default queue mapping uses the > > existing method that condsiders MSI irq vector. But the poll queue > > doesn't have an irq, so it uses the regular blk-mq cpu mapping. > > > > For verifying the improvement, I did Fio polling I/O performance test > > with io_uring engine with the options below. > > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N) > > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll > > queues for VM. > > > > As a result, IOPS and average latency improved about 10%. > > > > Test result: > > > > - Fio io_uring poll without virtio-blk poll support > > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us > > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us > > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us > > > > - Fio io_uring poll with virtio-blk poll support > > -- numjobs=1 : IOPS = 385K, avg latency = 165.94us > > -- numjobs=2 : IOPS = 408K, avg latency = 313.28us > > -- numjobs=4 : IOPS = 424K, avg latency = 613.05us > > > > Signed-off-by: Suwan Kim > > --- > > drivers/block/virtio_blk.c | 112 +++++++++++++++++++++++++++++++++++-- > > 1 file changed, 108 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > index 8c415be86732..712579dcd3cc 100644 > > --- a/drivers/block/virtio_blk.c > > +++ b/drivers/block/virtio_blk.c > > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues, > > "0 for no limit. " > > "Values > nr_cpu_ids truncated to nr_cpu_ids."); > > > > +static unsigned int poll_queues; > > +module_param(poll_queues, uint, 0644); > > +MODULE_PARM_DESC(poll_queues, "The number of dedicated virtqueues for polling I/O"); > > + > > static int major; > > static DEFINE_IDA(vd_index_ida); > > > > @@ -81,6 +85,7 @@ struct virtio_blk { > > > > /* num of vqs */ > > int num_vqs; > > + int io_queues[HCTX_MAX_TYPES]; > > struct virtio_blk_vq *vqs; > > }; > > > > @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk) > > const char **names; > > struct virtqueue **vqs; > > unsigned short num_vqs; > > + unsigned int num_poll_vqs; > > struct virtio_device *vdev = vblk->vdev; > > struct irq_affinity desc = { 0, }; > > > > @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk) > > &num_vqs); > > if (err) > > num_vqs = 1; > > + > > if (!err && !num_vqs) { > > dev_err(&vdev->dev, "MQ advertised but zero queues reported\n"); > > return -EINVAL; > > @@ -565,6 +572,18 @@ static int init_vq(struct virtio_blk *vblk) > > min_not_zero(num_request_queues, nr_cpu_ids), > > num_vqs); > > > > + num_poll_vqs = min_t(unsigned int, poll_queues, num_vqs - 1); > > + > > + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES); > > + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs; > > + vblk->io_queues[HCTX_TYPE_READ] = 0; > > + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs; > > + > > + dev_info(&vdev->dev, "%d/%d/%d default/read/poll queues\n", > > + vblk->io_queues[HCTX_TYPE_DEFAULT], > > + vblk->io_queues[HCTX_TYPE_READ], > > + vblk->io_queues[HCTX_TYPE_POLL]); > > + > > vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL); > > if (!vblk->vqs) > > return -ENOMEM; > > @@ -578,8 +597,13 @@ static int init_vq(struct virtio_blk *vblk) > > } > > > > for (i = 0; i < num_vqs; i++) { > > + if (i < num_vqs - num_poll_vqs) { > > + callbacks[i] = virtblk_done; > > + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i); > > + } else { > > + callbacks[i] = NULL; > > + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i); > > + } > > names[i] = vblk->vqs[i].name; > > This would look a little cleaner with two loops: > > for (i = 0; i < num_vqs - num_poll_vqs; i++) { > callbacks[i] = virtblk_done; > snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i); > names[i] = vblk->vqs[i].name; > } > for (; i < num_vqs; i++) { > callbacks[i] = NULL; > snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i); > names[i] = vblk->vqs[i].name; > } > It looks better. I will fix it. > > + > > + if (map->nr_queues == 0) > > + continue; > > + > > + /* > > + * Regular queues have interrupts and hence CPU affinity is > > + * defined by the core virtio code, but polling queues have > > + * no interrupts so we let the block layer assign CPU affinity. > > + */ > > + if (i == HCTX_TYPE_DEFAULT) > > I'd check for > i != HCTX_TYPE_POLL > > here instead to make the check a little more explicit and future proof > for the potential addition of read queues (which would be a Linux only > change without hypervisor or spec changes). In fact you might as well > add that support now as doing it is completely trivial once a driver > supports multiple map types. Your if condition is better choice when we consider future use of read queue. I will fix it too. > > +static void virtblk_complete_batch(struct io_comp_batch *iob) > > +{ > > + struct request *req; > > + struct virtblk_req *vbr; > > + > > + rq_list_for_each(&iob->req_list, req) { > > + vbr = blk_mq_rq_to_pdu(req); > > + virtblk_unmap_data(req, vbr); > > + virtblk_cleanup_cmd(req); > > vbr is only used ones, so why not just: > > virtblk_unmap_data(req, blk_mq_rq_to_pdu); > ? > Or even better add a cleanup patch to just remove the vbr argument to > virtblk_unmap_data as it is not needed at all. Thanks for the feedback. I will add cleanup patch in this series. Ragards, Suwan Kim