RE: [PATCH] cpuidle-haltpoll: Disable kvm guest polling when mwait_idle is used

["Li,Rongqing" <lirongqing@baidu.com>]

> -----Original Message-----
> From: Thomas Gleixner <tglx@linutronix.de>
> Sent: Wednesday, December 7, 2022 7:41 PM
> To: Li,Rongqing <lirongqing@baidu.com>; Rafael J. Wysocki <rafael@kernel.org>
> Cc: mingo@redhat.com; bp@alien8.de; dave.hansen@linux.intel.com;
> x86@kernel.org; rafael@kernel.org; daniel.lezcano@linaro.org;
> peterz@infradead.org; akpm@linux-foundation.org; tony.luck@intel.com;
> jpoimboe@kernel.org; linux-kernel@vger.kernel.org; linux-pm@vger.kernel.org
> Subject: RE: [PATCH] cpuidle-haltpoll: Disable kvm guest polling when
> mwait_idle is used
> 
> On Wed, Dec 07 2022 at 10:49, Rongqing Li wrote:
> >> Before change, "sockperf ping-pong -i 127.0.0.1 -p 20001  --tcp " latency is:
> >> sockperf: Summary: Latency is 6.245 usec
> >>
> >> this patch, disable cpuidle-haltpoll
> >> sockperf: Summary: Latency is 4.671 usec
> >>
> >>
> >> using arch_cpu_idle() in default_enter_idle()
> >> sockperf: Summary: Latency is 4.285 usec
> >>
> >
> > When I did upper tests, I taskset sockperf server and client to
> > different cpus, so using arch_cpu_idle() in default_enter_idle() gets
> > better result.
> >
> > I test unixbench also, find that Don't loading cpuidle-haltholl can
> > get more performance on 8 cores (2 threads per core) intel cpu which
> > cstate is disabled in host
> >
> > Don't load cpuidle-haltpoll:
> > System Benchmarks Index Score
> 1995.8
> > System Benchmarks Index Score
> 8482.8
> >
> > Replace default_idle with arch_cpu_idle, and load cpuidle-haltpoll, code like
> below:
> > System Benchmarks Index Score
> 1971.4
> > System Benchmarks Index Score
> 8467.7
> >
> > So I think we should not load cpuidle-haltpoll driver when guest has
> > mwait
> 
> So in the above you got:
> 
> Driver loaded not modified:     6.245
> Driver not loaded:              4.671           ~25%
> Driver loaded modified:         4.285           ~30%
> 
> Now with unixbench:
> 
> Driver not loaded:              8482.8
> Driver loaded modified:         8467.7          ~0.2%
> 
> So because of 0.2% delta you justify to throw away a 5% win?
> 
> If you really care about the 0.2%, then blacklist the module for your use case.
> 

Ok, Build it as module by default

Thanks

-Li