[DMARC FAILURE] Re: Compiler threads

[Stefan Reich]

Yeah i think I see the point. Is it calculated without a constant factor?
Just round up the result?

On Mon, Oct 14, 2019, 15:36 Doerr, Martin <martin.doerr at sap.com> wrote:

> Hi Stefan,
>
> > log(N CPUs) * log(log(N CPUs) << that's pretty amazing though
> This formula is from a time before UseDynamicNumberOfCompilerThreads was
> introduced.
> I guess people usually don't want to spend all their hardware threads for
> JIT compilation,
> but it may be beneficial to use a higher value depending on your scenario.
> With UseDynamicNumberOfCompilerThreads, CICompilerCount sets the upper
> limit. The JVM will dynamically add and remove threads between 1 per type
> and 1/3 for C1 2/3 for C2 of this value in total.
>
> Best regards,
> Martin
>
>
> > -----Original Message-----
> > From: hotspot-dev <hotspot-dev-bounces at openjdk.java.net> On Behalf Of
> > Stefan Reich
> > Sent: Sonntag, 13. Oktober 2019 19:52
> > To: Volker Simonis <volker.simonis at gmail.com>
> > Cc: hotspot-dev Source Developers <hotspot-dev at openjdk.java.net>
> > Subject: [DMARC FAILURE] Re: Compiler threads
> >
> > Hi Volker,
> >
> > OK, so it seems the answer is basically "It's complicated, but we have
> > spent a lot of thought on sensible defaults"... :-)
> >
> > log(N CPUs) * log(log(N CPUs) << that's pretty amazing though
> >
> > Thanks,
> > Stefan
> >
> > On Sun, 13 Oct 2019 at 19:48, Volker Simonis <volker.simonis at gmail.com>
> > wrote:
> >
> > > Hi Stefan,
> > >
> > > the answer to your questions depends a little bit on the Java version
> > > you are using.
> > >
> > > In jdk8 you can use -XX:CICompilerCount=<n> to explicitly set the
> > > number of compiler threads and  "-XX:+CICompilerCountPerCPU" to
> > > automatically set the number of compiler threads to "1 compiler thread
> > > for log(N CPUs)". If you use tiered compilation, which is the default,
> > > the "AdvancedThresholdPolicy" compilation policy will be used (can be
> > > controlled with "-XX:CompilationPolicyChoice=<n>"), which
> > > automatically enables "CICompilerCountPerCPU" but sets the number of
> > > compiler threads to log(N CPUs) * log(log(N CPUs)).
> > >
> > > In general, the number of compiler threads when using tiered
> > > compilation is distributed such that 1/3 of the total compiler threads
> > > will be tier 1 (i.e. C1) compiler threads and 2/3 will be tier 2 (i.e.
> > > C2) compiler threads.
> > >
> > > With jdk11 this system has been reworked and made more dynamic by
> > > introducing the option "-XX:+UseDynamicNumberOfCompilerThreads"
> > which
> > > is active by default. It will automatically spawn new compiler
> > > threads, if the compilation queues get full (see
> > > https://bugs.openjdk.java.net/browse/JDK-8198756 and
> > > https://bugs.openjdk.java.net/browse/JDK-8201235 for a more detailed
> > > explanation of the parameter).
> > >
> > > Best regards,
> > > Volker
> > >
> > > On Sun, Oct 13, 2019 at 5:06 PM Stefan Reich
> > > <stefan.reich.maker.of.eye at googlemail.com> wrote:
> > > >
> > > > Just a quick question: How many compiler threads does HotSpot use?
> > Does
> > > it
> > > > depend on then number of Java threads running?
> > > >
> > > > For example: Let's say I want the fastest startup time possible for a
> > > > single-thread application, so I want parallel JIT compilation on,
> say, 7,
> > > > out of 8 cores. Is that possible?
> > > >
> > > > Many greetings,
> > > > Stefan
> > > >
> > > > --
> > > > Stefan Reich
> > > > BotCompany.de // Java-based operating systems
> > >
> >
> >
> > --
> > Stefan Reich
> > BotCompany.de // Java-based operating systems
>