From: Fam Zheng <famz@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: qemu-devel@nongnu.org, Kevin Wolf <kwolf@redhat.com>,
qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 2/6] libqos: add virtio used ring support
Date: Thu, 29 Jun 2017 16:39:15 +0800 [thread overview]
Message-ID: <20170629083915.GB19976@lemon.lan> (raw)
In-Reply-To: <20170628184724.21378-3-stefanha@redhat.com>
On Wed, 06/28 19:47, Stefan Hajnoczi wrote:
> Existing tests do not touch the virtqueue used ring. Instead they poll
> the virtqueue ISR register and peek into their request's device-specific
> status field.
>
> It turns out that the virtqueue ISR register can be set to 1 more than
> once for a single notification (see commit
> 83d768b5640946b7da55ce8335509df297e2c7cd "virtio: set ISR on dataplane
> notifications"). This causes problems for tests that assume a 1:1
> correspondence between the ISR being 1 and request completion.
>
> Peeking at device-specific status fields is also problematic if the
> device has no field that can be abused for EINPROGRESS polling
> semantics. This is the case if all the field's values may be set by the
> device; there's no magic constant left for polling.
>
> It's time to process the used ring for completed requests, just like a
> real virtio guest driver. This patch adds the necessary APIs.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
next prev parent reply other threads:[~2017-06-29 8:39 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-28 18:47 [Qemu-devel] [PATCH 0/6] virtio: use ioeventfd in TCG and qtest mode Stefan Hajnoczi
2017-06-28 18:47 ` [Qemu-devel] [PATCH 1/6] libqos: fix typo in virtio.h QVirtQueue->used comment Stefan Hajnoczi
2017-06-29 8:32 ` Fam Zheng
2017-06-28 18:47 ` [Qemu-devel] [PATCH 2/6] libqos: add virtio used ring support Stefan Hajnoczi
2017-06-29 8:39 ` Fam Zheng [this message]
2017-06-28 18:47 ` [Qemu-devel] [PATCH 3/6] tests: fix virtio-scsi-test ISR dependence Stefan Hajnoczi
2017-06-29 8:40 ` Fam Zheng
2017-06-28 18:47 ` [Qemu-devel] [PATCH 4/6] tests: fix virtio-blk-test " Stefan Hajnoczi
2017-06-29 8:55 ` Fam Zheng
2017-06-28 18:47 ` [Qemu-devel] [PATCH 5/6] tests: fix virtio-net-test " Stefan Hajnoczi
2017-06-29 8:56 ` Fam Zheng
2017-06-28 18:47 ` [Qemu-devel] [PATCH 6/6] virtio-pci: use ioeventfd even when KVM is disabled Stefan Hajnoczi
2017-06-29 8:57 ` Fam Zheng
2017-06-28 19:38 ` [Qemu-devel] [PATCH 0/6] virtio: use ioeventfd in TCG and qtest mode Eric Blake
2017-06-29 9:47 ` Kevin Wolf
2017-06-29 23:34 ` Michael S. Tsirkin
2017-06-30 10:27 ` Stefan Hajnoczi
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