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

From: Li,Rongqing
Date: Wed Dec 07 2022 - 05:53:19 EST


> 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 Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 45665777.0 3913.1
Double-Precision Whetstone 55.0 6808.3 1237.9
Execl Throughput 43.0 4498.0 1046.1
File Copy 1024 bufsize 2000 maxblocks 3960.0 1285429.0 3246.0
File Copy 256 bufsize 500 maxblocks 1655.0 343057.0 2072.9
File Copy 4096 bufsize 8000 maxblocks 5800.0 3750374.0 6466.2
Pipe Throughput 12440.0 2271618.8 1826.1
Pipe-based Context Switching 4000.0 166393.6 416.0
Process Creation 126.0 12845.8 1019.5
Shell Scripts (1 concurrent) 42.4 9470.2 2233.5
Shell Scripts (8 concurrent) 6.0 4526.6 7544.4
System Call Overhead 15000.0 2082221.1 1388.1
========
System Benchmarks Index Score 1995.8

System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 388552307.2 33295.0
Double-Precision Whetstone 55.0 98968.4 17994.2
Execl Throughput 43.0 42346.5 9848.0
File Copy 1024 bufsize 2000 maxblocks 3960.0 945510.0 2387.7
File Copy 256 bufsize 500 maxblocks 1655.0 246909.0 1491.9
File Copy 4096 bufsize 8000 maxblocks 5800.0 3394311.0 5852.3
Pipe Throughput 12440.0 21325271.3 17142.5
Pipe-based Context Switching 4000.0 2746301.9 6865.8
Process Creation 126.0 94459.6 7496.8
Shell Scripts (1 concurrent) 42.4 62378.6 14711.9
Shell Scripts (8 concurrent) 6.0 8841.4 14735.7
System Call Overhead 15000.0 8850338.7 5900.2
========
System Benchmarks Index Score 8482.8



Replace default_idle with arch_cpu_idle, and load cpuidle-haltpoll, code like below:

@@ -32,7 +33,7 @@ static int default_enter_idle(struct cpuidle_device *dev,
local_irq_enable();
return index;
}
- default_idle();
+ arch_cpu_idle();
return index;
}
Result is below:
System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 42647356.0 3654.4
Double-Precision Whetstone 55.0 6812.9 1238.7
Execl Throughput 43.0 4424.4 1028.9
File Copy 1024 bufsize 2000 maxblocks 3960.0 1297513.0 3276.5
File Copy 256 bufsize 500 maxblocks 1655.0 346228.0 2092.0
File Copy 4096 bufsize 8000 maxblocks 5800.0 3902320.0 6728.1
Pipe Throughput 12440.0 2292292.4 1842.7
Pipe-based Context Switching 4000.0 163775.9 409.4
Process Creation 126.0 12216.8 969.6
Shell Scripts (1 concurrent) 42.4 9375.4 2211.2
Shell Scripts (8 concurrent) 6.0 4395.2 7325.3
System Call Overhead 15000.0 2030942.7 1354.0
========
System Benchmarks Index Score 1971.4

System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 390316671.8 33446.2
Double-Precision Whetstone 55.0 98945.1 17990.0
Execl Throughput 43.0 39600.0 9209.3
File Copy 1024 bufsize 2000 maxblocks 3960.0 939526.0 2372.5
File Copy 256 bufsize 500 maxblocks 1655.0 256813.0 1551.7
File Copy 4096 bufsize 8000 maxblocks 5800.0 3431020.0 5915.6
Pipe Throughput 12440.0 21320118.9 17138.4
Pipe-based Context Switching 4000.0 2743588.5 6859.0
Process Creation 126.0 94142.2 7471.6
Shell Scripts (1 concurrent) 42.4 62425.0 14722.9
Shell Scripts (8 concurrent) 6.0 8841.3 14735.5
System Call Overhead 15000.0 8864145.2 5909.4
========
System Benchmarks Index Score 8467.7


So I think we should not load cpuidle-haltpoll driver when guest has mwait

What's your suggestion

Thanks

-Li