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 3496FC4321E for ; Tue, 5 Apr 2022 20:10:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237599AbiDET7P (ORCPT ); Tue, 5 Apr 2022 15:59:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1449579AbiDEPuM (ORCPT ); Tue, 5 Apr 2022 11:50:12 -0400 Received: from mail-pl1-x630.google.com (mail-pl1-x630.google.com [IPv6:2607:f8b0:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9401056C01 for ; Tue, 5 Apr 2022 07:35:11 -0700 (PDT) Received: by mail-pl1-x630.google.com with SMTP id c23so11110768plo.0 for ; Tue, 05 Apr 2022 07:35:11 -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=M1XO7lnPB/LA5in3rTfbTME8v5xLGtJ4KRhZSZNsXnY=; b=c+g1oisbGJ1/N0TGmKf3JvD+SdQ/KzFFxh6EDnioo8Be+lSIiB4XUpuuS+clL3cT9r y0lMemsn7UGEB7je9AFQMZ5oW8DhupzPFZKZ4MYSyF/6H1yrm5E+tmHP8WpoWw/Pg6Ns vKVMI3cfwax7+cur4mbVkORSwp+CUgN2dg01DNjLc8oHcw8876xSVDJZIHi50L2+7tlj w2XvGKqkxCIrgxVHBySfX/HbGnmLTMnrPFkwTXt53GK2hKZ5RHxtTo+K2IfuRpbyTKJB g0fFKUTh7D8JgX7S5/xvFmQSMzs4b7QXdae4QC8nJdZfJu/QL5K2Kkc0jAoMGb3pohTE fu/A== 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=M1XO7lnPB/LA5in3rTfbTME8v5xLGtJ4KRhZSZNsXnY=; b=qDcYg+hn9ZW53pCofE8mkWyDMxLj8ZYvzbU5hiBLzTUhGYKqQdV3WyUq8Jv2tsu+Wd NAPbPFYfJJFNZazpyRo95zARlBAVQJvob42Y6ia3NuCGyPTfYeCGha0Mk1myUXjzBLxg 23NdR9qmIMOxDnooiNb49Yzgdl18JtpJtCjN1SbVvYGHW02mPGRPqNKON7NFY2nsfbbG BaNpoSStngMsmHDvu2WxxnVfMfAOu+R4/8dbajyJiuHnTglLMXy1vv2Z2Bf6YwOgVa3d Y2ihSUd4wPN89YT35ss8A3Xxa8rIX8zWIbRkuE9YrkuWidqfUyWrJ/JvNf1S1mBJbhVh nfKA== X-Gm-Message-State: AOAM532+Hc9Yx7yZ6AnLYHE8RXqLGXJ8nWsnSLM4goy7kO0Lobi4f8zC gWuiuHDPUMbPmhioE33zIwM= X-Google-Smtp-Source: ABdhPJx7jw6DmUGeLLcqbVa8sN4KZ6uMDQCT5t9FIZqcLtAh3/HbPhklIVwuSYF8uHRXJOVAzd83kQ== X-Received: by 2002:a17:902:cec9:b0:156:8e7a:bf4e with SMTP id d9-20020a170902cec900b001568e7abf4emr3809803plg.62.1649169310840; Tue, 05 Apr 2022 07:35:10 -0700 (PDT) Received: from localhost.localdomain ([114.200.4.15]) by smtp.gmail.com with ESMTPSA id m17-20020a17090a859100b001bc20ddcc67sm2585799pjn.34.2022.04.05.07.35.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Apr 2022 07:35:09 -0700 (PDT) Date: Tue, 5 Apr 2022 23:35:03 +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; > } > > > + > > + 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. > > > +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. I replied that I will add cleanup path but after thinking about it again, it seems better not to remove the argument because blk_mq_rq_to_pdu() needs type casting anyway. So I will fix it to "virtblk_unmap_data(req, blk_mq_rq_to_pdu);" as you mentioned. Regards, Suwan Kim