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
