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

From: Jason Wang
Date: Sun Jan 06 2019 - 22:53:55 EST

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
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

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


no smap being before or after?

Let me clarify:

Before (SMAP on): 5.0Mpps

Before (SMAP off): 7.5Mpps

After (SMAP on): 6.1Mpps