[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index
From: |
Jes Sorensen |
Subject: |
Re: [Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself |
Date: |
Wed, 02 Jun 2010 22:39:02 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Lightning/1.0b2pre Thunderbird/3.0.4 |
On 05/31/10 09:46, Rusty Russell wrote:
> On Thu, 27 May 2010 05:20:35 am Michael S. Tsirkin wrote:
>> Here's a rewrite of the original patch with a new layout.
>> I haven't tested it yet so no idea how this performs, but
>> I think this addresses the cache bounce issue raised by Avi.
>> Posting for early flames/comments.
>
> Sorry, not without some evidence that it'll actually reduce cacheline
> bouncing. I *think* it will, but it's not obvious: the host may keep
> looking at avail_idx as we're updating last_seen. Or does qemu always
> look at both together anyway?
>
> Can someone convince me this is a win?
> Rusty.
Hi Rusty,
I ran some tests using the vring index publish patch with virtio_blk.
The numbers are based on running IOZone on a ramdisk passed to the guest
via virtio. While I didn't see any throughput improvements, I saw a
20-30% reduction in the VMExit count for the full run. This was measured
grabbing the VMExit count prior and after the run and calculating the
difference.
I have the numbers in a PDF, so I will email it to you in private as I
don't like sending PDFs to the mailing list. However if anybody else
wants the numbers feel free to ping me off list and I'll forward them.
Cheers,
Jes
[Prev in Thread] |
Current Thread |
[Next in Thread] |
- Re: [Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself,
Jes Sorensen <=