From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EEA341F461A for ; Mon, 20 Oct 2025 15:18:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760973506; cv=none; b=RRMKvqTDzIf1t/UlS1+fN+PBzuNoLRITeLeDaPESsyKWPeU84XvmM9D9ikzCRjuKvGTFqTCAC2i1I4a9/6h9ERixNT3PB5nadk0S8yz+d+KQ/a+YggSMF4M7rGkKqQ9NMzwT/hDNCDYKTlSIJfPnIrrPOYEow0p/F7kFWZdRmKU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760973506; c=relaxed/simple; bh=vxeZU8BIk7yt5+gefMlL/GNoEVo0y7v8NbR4bXP2d6A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=N0z02MZ005Ik7ZXlxWOsilKw7i2ZQNvMPtYNrldKtYXy+EGb7s5EusTSg+bjDdI3Zy/pQ4gRSd92hMAalW8/AUM7MtEOOdetoY7iLXcZTlzaN3fn565BcKUDnEGABUTfWzq2ZeeHQ6+hiKVmu4uP73xVBviAiYRjvIVIC3fwDh4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=EomVYDqA; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EomVYDqA" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760973504; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=376JEJXXuhTvk7uwIbwEp0J9xIBggDxY0JbNoKssPdI=; b=EomVYDqAmKLyV8pm+NHzq4YWOnMpiI37iPRmM7T6OyYeWgpxMVoMFVIIfXdAZHx5TtEKOv KT7ztxm+e0xziVO5JjiajdxrR6+kPiA5TMI9baQgHBb/HNXOqDdcRSwJI8BawkKwuoXSXd 1zPDqyiqYv3JanRruP+EPYSJz4Hf7oo= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-561-SPLa6nX0MqG6BDyiQWw_SQ-1; Mon, 20 Oct 2025 11:18:22 -0400 X-MC-Unique: SPLa6nX0MqG6BDyiQWw_SQ-1 X-Mimecast-MFC-AGG-ID: SPLa6nX0MqG6BDyiQWw_SQ_1760973501 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-47105bfcf15so24641295e9.2 for ; Mon, 20 Oct 2025 08:18:22 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1760973501; x=1761578301; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=376JEJXXuhTvk7uwIbwEp0J9xIBggDxY0JbNoKssPdI=; b=wKwoQHUY1Ddvo3odKJCFVXc1y+LFR+yLn8xtsVPLnyNrGYimiBSJYvDAz2DUJGTNR1 J4tTae/5Pug22pcOdJDViMRR/Aob93qtb1snX45/a2i4mq9Yl4ILYTSQvrtQza3zVEc0 +T2FOsc//Ba54ydjyTlRpy0qauTB3wGjEGWeN9LDJW+HK43RXMKICAOiuPFJW7abgBMD +5IyBIbzV3XYw6yI//P4jOv/14k7A7EA8lhrlr/RJODCOj2NxXngIQ2hFlJJkEuDDgvZ ETHw26KPagf+frx9IByy80Zgb3+XYKSeNmsb8wlIBhTKdK/ztzIdpGQZAhbvNzVtxbaG wlOg== X-Forwarded-Encrypted: i=1; AJvYcCX5CYXT+CERfrUYPfR1edH08ZFLOPnOHb60H4y5Ga+yz/zz0lBN8Sl5OODCJQUxhtV/oNNq1opu08qpJNM=@vger.kernel.org X-Gm-Message-State: AOJu0YzOu/9dQKFrL5N/5ieRdcBSeoaHOTO/I2Hj7f1J3dzbfXeLgAh/ 8ySARBp7wDdIw+8hjJMaG85YtUCD7UkUYtV5jxX0u+B6LIdRmqW7YQDXlIvDhTEK9lidIfZuMHy 2kKxUiyfvKdVC0mDF2GT1xuqrzVxSO4+qitRtYwvDccS//jEyhkNhwJRIEySGGScmLWh0UTo0NQ == X-Gm-Gg: ASbGncvuCfh8M5GDWwJVORhm1Ri4HJFchRsQrIC+7ODBS/IDXjGEEZ0OOAQDkJLQo6J cdWJLoq9AX4ikU9RJVEfrrNo/ZjrKHPqIKxRDdK3FBcs4EImLXHd5kQ40ZYLZXVTQnCUPe9ZrX5 Sewn0PumksznByNa4YfYpN8pV+D5rrVyznAyhcTcReIBmO2eNSJQf8PZF7MbDeH1ffm7fiblwC2 3FnuJNLwYDZ7NfyNHh0UQdnvLjU0H5M8GKqQyD2HOnHePCEyvElst0U5294hkJ8Sxm9PZ5qS5IK sUJKRuZzHrM86IJWVztunsoilS3O+w51cOEE4UlFGyi94SqM0lTOAddz7MyzxQ7Rt6PM X-Received: by 2002:a05:600c:3f08:b0:470:ffd1:782d with SMTP id 5b1f17b1804b1-47117876a19mr111618955e9.6.1760973501154; Mon, 20 Oct 2025 08:18:21 -0700 (PDT) X-Google-Smtp-Source: AGHT+IETLd9da+Ou77Y8StkQ2q014OfnaoUD42+rUXfxhJ8RF6vKnDc5lJ9/jBhXf+wCuZ6ndVoZBw== X-Received: by 2002:a05:600c:3f08:b0:470:ffd1:782d with SMTP id 5b1f17b1804b1-47117876a19mr111618715e9.6.1760973500619; Mon, 20 Oct 2025 08:18:20 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:152d:b200:2a90:8f13:7c1e:f479]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-471553f8a3asm174428685e9.16.2025.10.20.08.18.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Oct 2025 08:18:20 -0700 (PDT) Date: Mon, 20 Oct 2025 11:18:17 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH V8 14/19] virtio_ring: determine descriptor flags at one time Message-ID: <20251020110341-mutt-send-email-mst@kernel.org> References: <20251020071003.28834-1-jasowang@redhat.com> <20251020071003.28834-15-jasowang@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20251020071003.28834-15-jasowang@redhat.com> On Mon, Oct 20, 2025 at 03:09:58PM +0800, Jason Wang wrote: > Let's determine the last descriptor by counting the number of sg. This > would be consistent with packed virtqueue implementation and ease the > future in-order implementation. > > Acked-by: Eugenio Pérez > Reviewed-by: Xuan Zhuo > Signed-off-by: Jason Wang > --- > drivers/virtio/virtio_ring.c | 19 ++++++------------- > 1 file changed, 6 insertions(+), 13 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 37b16ef906a4..20bc48b1241e 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -575,7 +575,7 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq, > struct vring_desc_extra *extra; > struct scatterlist *sg; > struct vring_desc *desc; > - unsigned int i, n, avail, descs_used, prev, err_idx; > + unsigned int i, n, avail, descs_used, err_idx, c = 0; > int head; > bool indirect; > c is not a great variable name. Maybe sg_count? same in patch 19 actually. > @@ -639,12 +639,11 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq, > if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, &addr, &len, premapped)) > goto unmap_release; > > - prev = i; > /* Note that we trust indirect descriptor > * table since it use stream DMA mapping. > */ > i = virtqueue_add_desc_split(vq, desc, extra, i, addr, len, > - VRING_DESC_F_NEXT, > + ++c == total_sg ? 0 : VRING_DESC_F_NEXT, > premapped); > } > } > @@ -656,21 +655,15 @@ static inline int virtqueue_add_split(struct vring_virtqueue *vq, > if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, &addr, &len, premapped)) > goto unmap_release; > > - prev = i; > /* Note that we trust indirect descriptor > * table since it use stream DMA mapping. > */ > - i = virtqueue_add_desc_split(vq, desc, extra, i, addr, len, > - VRING_DESC_F_NEXT | > - VRING_DESC_F_WRITE, > - premapped); > + i = virtqueue_add_desc_split(vq, desc, extra, > + i, addr, len, > + (++c == total_sg ? 0 : VRING_DESC_F_NEXT) | > + VRING_DESC_F_WRITE, premapped); this continuation line should be indented more, and maybe premapped on a line by itself. Alternatively use a variable for flags. > } > } > - /* Last one doesn't continue. */ > - desc[prev].flags &= cpu_to_virtio16(vq->vq.vdev, ~VRING_DESC_F_NEXT); > - if (!indirect && vring_need_unmap_buffer(vq, &extra[prev])) > - vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &= > - ~VRING_DESC_F_NEXT; > > if (indirect) { > /* Now that the indirect table is filled in, map it. */ > -- > 2.31.1