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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Li,Rongqing" <lirongqing@baidu.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>
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        "rafael@kernel.org" <rafael@kernel.org>,
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Subject: RE: [PATCH] cpuidle-haltpoll: Disable kvm guest polling when
 mwait_idle is used
In-Reply-To: <59bf331606fc4d68a8aa866c50c902be@baidu.com>
References: <1670308998-12313-1-git-send-email-lirongqing@baidu.com>
 <CAJZ5v0gG93BXZWOcRVpng_EN-h4+sOyUqTc1XRt4xZkqMnaZZw@mail.gmail.com>
 <87mt80g2fp.ffs@tglx> <59bf331606fc4d68a8aa866c50c902be@baidu.com>
Date:   Wed, 07 Dec 2022 12:41:16 +0100
Message-ID: <875yenfnkz.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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.

Thanks,

        tglx