On 2017/8/29 22:56, Michael S. Tsirkin wrote:
On Tue, Aug 29, 2017 at 11:46:34AM +0000, Yang Zhang wrote:
Some latency-intensive workload will see obviously performance
drop when running inside VM.
But are we trading a lot of CPU for a bit of lower latency?
The main reason is that the overhead
is amplified when running inside VM. The most cost i have seen is
inside idle path.
This patch introduces a new mechanism to poll for a while before
entering idle state. If schedule is needed during poll, then we
don't need to goes through the heavy overhead path.
Isn't it the job of an idle driver to find the best way to
halt the CPU?
It looks like just by adding a cstate we can make it
halt at higher latencies only. And at lower latencies,
if it's doing a good job we can hopefully use mwait to
stop the CPU.
In fact I have been experimenting with exactly that.
Some initial results are encouraging but I could use help
with testing and especially tuning. If you can help
pls let me know!
Quan, Can you help to test it and give result? Thanks.
--
Yang
Alibaba Cloud Computing
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