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Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring
From: |
Rusty Russell |
Subject: |
Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself |
Date: |
Fri, 7 May 2010 12:53:52 +0930 |
User-agent: |
KMail/1.13.2 (Linux/2.6.32-21-generic; KDE/4.4.2; i686; ; ) |
On Thu, 6 May 2010 07:30:00 pm Avi Kivity wrote:
> On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote:
> > + /* We publish the last-seen used index at the end of the available ring.
> > + * It is at the end for backwards compatibility. */
> > + vr->last_used_idx =&(vr)->avail->ring[num];
> > + /* Verify that last used index does not spill over the used ring. */
> > + BUG_ON((void *)vr->last_used_idx +
> > + sizeof *vr->last_used_idx> (void *)vr->used);
> > }
> >
>
> Shouldn't this be on its own cache line?
It's next to the available ring; because that's where the guest publishes
its data. That whole page is guest-write, host-read.
Putting it on a cacheline by itself would be a slight pessimization; the host
cpu would have to get the last_used_idx cacheline and the avail descriptor
cacheline every time. This way, they are sometimes the same cacheline.
Hope that clarifies,
Rusty.
- [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/05
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/06
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself,
Rusty Russell <=
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/11
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/11
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Rusty Russell, 2010/05/19
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/19
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/19
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Rusty Russell, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Rusty Russell, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/23