On 2017-11-16 05:31, Konrad Rzeszutek Wilk wrote:
> On Mon, Nov 13, 2017 at 06:05:59PM +0800, Quan Xu wrote:
>> From: Yang Zhang <[email protected]>
>>
>> Some latency-intensive workload have seen obviously performance
>> drop when running inside VM. The main reason is that the overhead
>> is amplified when running inside VM. The most cost I have seen is
>> inside idle path.
> Meaning an VMEXIT b/c it is an 'halt' operation ? And then going
> back in guest (VMRESUME) takes time. And hence your latency gets
> all whacked b/c of this?
Konrad, I can't follow 'b/c' here.. sorry.
> So if I understand - you want to use your _full_ timeslice (of the guest)
> without ever (or as much as possible) to go in the hypervisor?
as much as possible.
> Which means in effect you don't care about power-saving or CPUfreq
> savings, you just want to eat the full CPU for snack?
actually, we care about power-saving. The poll duration is
self-tuning, otherwise it is almost as the same as
'halt=poll'. Also we always sent out with CPU usage of benchmark
netperf/ctxsw. We got much more
performance with limited promotion of CPU usage.
>> 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.
> Schedule of what? The guest or the host?
rescheduled of guest scheduler..
it is the guest.
Quan
Alibaba Cloud
>
>
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