Messages in this thread | | | Subject | Re: [RFC PATCH V3 0/5] Hi: | From | Jason Wang <> | Date | Mon, 7 Jan 2019 11:53:41 +0800 |
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On 2019/1/7 上午11:28, Michael S. Tsirkin wrote: > On Mon, Jan 07, 2019 at 10:19:03AM +0800, Jason Wang wrote: >> On 2019/1/3 上午4:47, 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
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