Avi Kivity wrote: > On 08/26/2009 04:01 AM, Gregory Haskins wrote: >> We are pleased to announce the availability of the latest networking >> benchmark numbers for AlacrityVM. We've made several tweaks to the >> original v0.1 release to improve performance. The most notable is a >> switch from get_user_pages to switch_mm+copy_[to/from]_user thanks to a >> review suggestion from Michael Tsirkin (as well as his patch to >> implement it). >> >> This change alone accounted for freeing up an additional 1.2Gbps, which >> is over 25% improvement from v0.1. The previous numbers were 4560Gbps >> before the change, and 5708Gbps after (for 1500mtu over 10GE). This >> moves us ever closer to the goal of native performance under >> virtualization. >> > > Interesting, it's good to see that copy_*_user() works so well. Note > that there's a possible optimization that goes in the opposite direction > - keep using get_user_pages(), but use the dma engine API to perform the > actual copy. I expect that it will only be a win when using tso to > transfer full pages. Large pages may also help. > > Copyless tx also wants get_user_pages(). It makes sense to check if > switch_mm() + get_user_pages_fast() gives better performance than > get_user_pages(). Actually, I have already look at this and it does indeed seem better to use switch_mm+gupf() over gup() by quite a large margin. You could then couple that with your DMA-engine idea to potentially gain even more benefits (though probably not for networking since most NICs have their own DMA engine anyway). Kind Regards, -Greg
Attachment:
signature.asc
Description: OpenPGP digital signature
