RFR: 8307766: Linux: Provide the option to override the timer slack

[David Holmes]

On Tue, 9 May 2023 15:36:11 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See the description in the RFE.
> 
> On `c6.8xlarge`, the sleep accuracy is improved the following way:
> 
> 
> % CONF=linux-x86_64-server-release make test TEST=micro:ThreadSleep.millisNanos
> 
> Benchmark                   (sleep)  Mode  Cnt           Score      Error  Units
> 
> # Default
> ThreadSleep.millisNanos           0  avgt   15         473.727 ±    3.542  ns/op
> ThreadSleep.millisNanos           1  avgt   15         585.868 ±    2.010  ns/op
> ThreadSleep.millisNanos          10  avgt   15         583.475 ±    1.426  ns/op
> ThreadSleep.millisNanos         100  avgt   15       57833.073 ±  146.406  ns/op
> ThreadSleep.millisNanos        1000  avgt   15       59324.901 ±  620.924  ns/op
> ThreadSleep.millisNanos       10000  avgt   15       68071.990 ±  537.880  ns/op
> ThreadSleep.millisNanos      100000  avgt   15      158069.170 ±  329.991  ns/op
> ThreadSleep.millisNanos     1000000  avgt   15     1059044.770 ±  370.982  ns/op
> ThreadSleep.millisNanos    10000000  avgt   15    10060017.354 ±  399.309  ns/op
> ThreadSleep.millisNanos   100000000  avgt   15   100062969.073 ± 2399.053  ns/op
> ThreadSleep.millisNanos  1000000000  avgt   15  1000068474.467 ± 2669.980  ns/op
> 
> # -XX:TimerSlack=1
> ThreadSleep.millisNanos           0  avgt   15         469.632 ±    1.500  ns/op
> ThreadSleep.millisNanos           1  avgt   15         587.562 ±    8.966  ns/op
> ThreadSleep.millisNanos          10  avgt   15         584.241 ±    1.997  ns/op
> ThreadSleep.millisNanos         100  avgt   15        7907.160 ±   12.476  ns/op
> ThreadSleep.millisNanos        1000  avgt   15        7913.984 ±   56.996  ns/op
> ThreadSleep.millisNanos       10000  avgt   15       17929.107 ±  432.083  ns/op
> ThreadSleep.millisNanos      100000  avgt   15      108154.851 ±  403.717  ns/op
> ThreadSleep.millisNanos     1000000  avgt   15     1008854.095 ±  418.444  ns/op
> ThreadSleep.millisNanos    10000000  avgt   15    10009902.829 ±  279.617  ns/op
> ThreadSleep.millisNanos   100000000  avgt   15   100014000.020 ± 2143.820  ns/op
> ThreadSleep.millisNanos  1000000000  avgt   15  1000020734.333 ± 4846.754  ns/op

src/hotspot/os/linux/globals_linux.hpp line 82:

> 80:           "Write map file for Linux perf tool at exit")                 \
> 81:                                                                         \
> 82:   product(intx, TimerSlack, -1, EXPERIMENTAL,                           \

Why experimental? Is this not something that these users want to use in production?

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PR Review Comment: https://git.openjdk.org/jdk/pull/13889#discussion_r1199866198