Re: [RFC PATCH V3 0/5] Hi:

[Jason Wang]

On 2019/1/7 äå11:28, Michael S. Tsirkin wrote:
> On Mon, Jan 07, 2019 at 10:19:03AM +0800, Jason Wang wrote:
> > On 2019/1/3 äå4:47, Michael S. Tsirkin wrote:
> > > On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:
> > > > This series tries to access virtqueue metadata through kernel virtual
> > > > address instead of copy_user() friends since they had too much
> > > > overheads like checks, spec barriers or even hardware feature
> > > > toggling.
> > > Will review, thanks!
> > > One questions that comes to mind is whether it's all about bypassing
> > > stac/clac.  Could you please include a performance comparison with
> > > nosmap?
> > On machine without SMAP (Sandy Bridge):
> >
> > Before: 4.8Mpps
> >
> > After: 5.2Mpps
> OK so would you say it's really unsafe versus safe accesses?
> Or would you say it's just a better written code?


It's the effect of removing speculation barrier.


> > On machine with SMAP (Broadwell):
> >
> > Before: 5.0Mpps
> >
> > After: 6.1Mpps
> >
> > No smap: 7.5Mpps
> >
> >
> > Thanks
>
> no smap being before or after?

Let me clarify:


Before (SMAP on): 5.0Mpps

Before (SMAP off): 7.5Mpps

After (SMAP on): 6.1Mpps


Thanks