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

Jason Wang
2019-01-25T09:16:32Z

On 2019/1/25 上午11:00, 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