On 2017/12/14 19:56, Paolo Bonzini wrote:
On 13/12/2017 17:28, Konrad Rzeszutek Wilk wrote:
1) VM idle path and network req/resp services:
Does this go away if you don't hit the idle path? Meaning if you
loop without hitting HLT/MWAIT? I am assuming the issue you are facing
is the latency - that is first time the guest comes from HLT and
responds to the packet the latency is much higher than without?
And the arming of the timer?
2) process context switches.
Is that related to the 1)? That is the 'schedule' call and the process
going to sleep waiting for an interrupt or timer?
This all sounds like issues with low-CPU usage workloads where you
need low latency responses?
Even high-CPU usage, as long as there is a small idle time. The cost of
setting the TSC deadline timer twice is about 3000 cycles.
However, I think Amazon's approach of not intercepting HLT/MWAIT/PAUSE
can recover most of the performance and it's way less intrusive.
Paolo, could you share the Amazon's patch or the LML link? thanks.
Quan
Thanks,
Paolo
