Strange interaction with hyperthreading on Intel hybrid CPU

[Francesco Nigro]

I suggest to use a profiler which can show more than the java side here,
async profiler.
But please beware the suggestion
https://github.com/async-profiler/async-profiler/issues/779#issuecomment-1651104553
from one of the Loom team's member.

Il mer 11 ott 2023, 18:54 Michael van Acken <michael.van.acken at gmail.com>
ha scritto:

> Given the huge difference of a factor of 2 in user time between the
> default and the nosmt setup, I tried to use jfr to find some metric that
> differs markedly between the two.  The workload is the same: the very same
> task is executed leading to the expected result.  This time it's 300 back
> to back compilations within a single java process.  Using the threadId() of
> a final virtual thread as proxy, ~570k threads seem to be utilized overall.
>
> "jfr view hot-methods" does not show any significant difference, with the
> top entry being ForkJoinPool.awaitWork() at around 5.5% in both cases.
>
> But "jfr view latencies-by-type" shows a large difference in its Total
> column for "Java Thread Park".  Could this be a clue where the user time
> accumulates?
>
> ### with "nosmt"
>
> real 77.67
> user 468.16
> sys 13.48
>
> jfr view latencies-by-type recording.jfr
>                                Latencies by Type
>
> Event Type                              Count Average    P 99 Longest
> Total
> -------------------------------------- ------ ------- ------- -------
> ---------
> Java Thread Park                       18.651 36,9 ms  310 ms  2,88 s 11 m
> 43 s
> File Write                                  2 11,7 ms 12,6 ms 12,6 ms
> 23,4 ms
>
> ### default (without "nosmt")
>
> real 93.60
> user 824.12
> sys 23.08
>
> jfr view latencies-by-type recording.jfr
>                                Latencies by Type
>
> Event Type                               Count Average    P 99 Longest
>  Total
> --------------------------------------- ------ ------- ------- -------
> --------
> Java Thread Park                        30.263 45,7 ms  256 ms  504 ms 23
> m 2 s
> File Read                                    1 10,9 ms 10,9 ms 10,9 ms
>  10,9 ms
>
>
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