Re: [PATCH net-next V4 5/5] vhost: access vq metadata through kernel virtual address

[Jason Wang]

On 2019/1/25 äå11:00, Michael S. Tsirkin wrote:
> On Thu, Jan 24, 2019 at 12:07:54PM +0800, Jason Wang wrote:
> > > Meanwhile, could you pls post data comparing this last patch with the
> > > below?  This removes the speculation barrier replacing it with a
> > > (useless but at least more lightweight) data dependency.
> > SMAP off
> >
> > Your patch: 7.2MPPs
> >
> > vmap: 7.4Mpps
> OK so while we keep looking into vmap, why don't we merge something like
> the below?  Seems quite straight forward ...

The problem is it gives ~8% regression on PPS when SMAP is on. This is 
probably because the latency of lfence is hided by previous stac as 
mentioned in the commit b3bbfb3fb5d25776b8e3f361d2eedaabb0b496cd.

Thanks