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From: Stefan Hajnoczi <stefanha@gmail.com>
To: Tiwei Bie <tiwei.bie@intel.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	"Wang, Zhihong" <zhihong.wang@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC] virtio: support VIRTIO_F_IO_BARRIER
Date: Thu, 3 May 2018 14:50:07 +0100	[thread overview]
Message-ID: <CAJSP0QUfvRH0SVMPZB_5xYa2LbSFy9jXe=c7v68AFMf01eSWuQ__40307.7885312543$1525355288$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <20180503132647.yfulyzbygdfgu2or@debian>

On Thu, May 3, 2018 at 2:26 PM, Tiwei Bie <tiwei.bie@intel.com> wrote:
> On Thu, May 03, 2018 at 10:06:52AM +0100, Stefan Hajnoczi wrote:
>> On Thu, May 03, 2018 at 10:59:55AM +0800, Tiwei Bie wrote:
>> > This patch introduces the support for VIRTIO_F_IO_BARRIER.
>> > When this feature is negotiated, driver will use the barriers
>> > suitable for hardware devices.
>> >
>> > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>
>> I should have thought of this earlier, but why is a new feature bit
>> necessary?  If a hardware virtio device is in use, then the device
>> should already negotiate VIRTIO_F_IOMMU_PLATFORM (i.e. use DMA APIs and
>> IOMMU callbacks).
>>
>> Does disabling weak_barriers when VIRTIO_F_IOMMU_PLATFORM is set solve
>> the problem?
>
> The VIRTIO_F_IOMMU_PLATFORM feature can be set when the
> device is implemented in software. And I think we don't
> want the performance drop in this case.

Good point.

Stefan

  parent reply	other threads:[~2018-05-03 13:50 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-03  2:59 [RFC] virtio: support VIRTIO_F_IO_BARRIER Tiwei Bie
2018-05-03  7:30 ` Jason Wang
2018-05-03  7:30   ` Jason Wang
2018-05-03  8:30   ` Tiwei Bie
2018-05-03  8:30   ` Tiwei Bie
2018-05-03  9:09     ` Jason Wang
2018-05-03  9:09     ` Jason Wang
2018-05-03  9:58       ` Tiwei Bie
2018-05-03  9:58       ` Tiwei Bie
2018-05-03 12:57         ` Jason Wang
2018-05-03 12:57         ` Jason Wang
2018-05-03  9:06 ` Stefan Hajnoczi
2018-05-03  9:06 ` Stefan Hajnoczi
2018-05-03 13:26   ` Tiwei Bie
2018-05-03 13:26     ` Tiwei Bie
2018-05-03 13:50     ` Stefan Hajnoczi
2018-05-03 13:50     ` Stefan Hajnoczi [this message]
2018-05-03 17:57 ` Michael S. Tsirkin
2018-05-04  1:14   ` Tiwei Bie
2018-05-04  1:14   ` Tiwei Bie
2018-05-03 17:57 ` Michael S. Tsirkin
2018-05-03  2:59 Tiwei Bie

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