From: Halil Pasic <pasic@linux.ibm.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>,
qemu-devel@nongnu.org, qemu-stable@nongnu.org
Subject: Re: [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM
Date: Wed, 26 Feb 2020 13:50:18 +0100 [thread overview]
Message-ID: <20200226135018.608185bb.pasic@linux.ibm.com> (raw)
In-Reply-To: <20200226064243-mutt-send-email-mst@kernel.org>
On Wed, 26 Feb 2020 06:44:25 -0500
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Wed, Feb 26, 2020 at 06:17:34PM +0800, Jason Wang wrote:
> >
> > On 2020/2/26 下午5:53, Michael S. Tsirkin wrote:
> > > On Wed, Feb 26, 2020 at 05:43:57PM +0800, Jason Wang wrote:
> > > > We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on
> > > > platform without IOMMU support. This can lead unnecessary IOTLB
> > > > transactions which will damage the performance.
> > > >
> > > > Fixing this by check whether the device is backed by IOMMU and disable
> > > > device IOTLB.
> > > >
> > > > Reported-by: Halil Pasic <pasic@linux.ibm.com>
> > > > Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support")
> > > Well it's just an optimization, isn't it?
> >
> >
> > Kind of, or a fix for the performance.
> >
>
> Given this wasn't a regression, it's a valuable enhancement
> but Fixes: seems to agressive.
IMHO Fixes is appropriate. Telling vhost-net F_ACCESS_PLATFORM
when when vdev->dma_as != &address_space_memory results in a severe
performance degradation.
Regards,
Halil
[..]
next prev parent reply other threads:[~2020-02-26 12:51 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 9:43 [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM Jason Wang
2020-02-26 9:53 ` Michael S. Tsirkin
2020-02-26 10:17 ` Jason Wang
2020-02-26 11:44 ` Michael S. Tsirkin
2020-02-26 12:50 ` Halil Pasic [this message]
2020-02-26 12:55 ` Halil Pasic
2020-02-26 13:45 ` Michael S. Tsirkin
2020-02-26 13:28 ` Halil Pasic
2020-02-26 13:37 ` Michael S. Tsirkin
2020-02-26 15:36 ` Halil Pasic
2020-02-26 16:52 ` Michael S. Tsirkin
2020-02-27 13:02 ` Halil Pasic
2020-02-27 15:47 ` Michael S. Tsirkin
2020-03-03 14:44 ` Halil Pasic
2020-03-13 12:44 ` Halil Pasic
2020-03-13 15:29 ` Michael S. Tsirkin
2020-03-13 16:31 ` Peter Xu
2020-03-16 16:57 ` Halil Pasic
2020-03-16 17:31 ` Peter Xu
2020-03-16 17:19 ` Michael S. Tsirkin
2020-03-16 18:14 ` Peter Xu
2020-03-17 3:04 ` Jason Wang
2020-03-17 14:13 ` Peter Xu
2020-03-18 2:06 ` Jason Wang
2020-03-17 6:28 ` Michael S. Tsirkin
2020-03-17 14:39 ` Peter Xu
2020-03-17 14:55 ` Michael S. Tsirkin
2020-03-13 20:27 ` Brijesh Singh
2020-03-14 18:22 ` Michael S. Tsirkin
2020-02-27 20:36 ` Tom Lendacky
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