RFR: 8307766: Linux: Provide the option to override the timer slack [v5]

[David Holmes]

On Wed, 28 Jun 2023 17:27:27 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
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8307766-linux-timer-slack
>  - Touchup comment again
>  - Touch-up the comment
>  - Review comments
>  - Merge branch 'master' into JDK-8307766-linux-timer-slack
>  - Fix

As this is experimental and seems non-intrusive I can approve it. But how will this be tested? Can we at least sanity check setting it and reading back the value we set?

Thanks.

-------------

PR Review: https://git.openjdk.org/jdk/pull/13889#pullrequestreview-1504416545