RFR: JDK-8202384: Introduce altserver jvm variant with

[Erik Joelsson]

Hello Matthias,

For GCC, you need 7.3.0 or later. For Microsoft you need VS2017 and I 
think some minimal update version (the option is called -Qspectre), we 
use 15.5.5.

I was not involved in the benchmarking so I don't know any details 
there, only the conclusion.

/Erik


On 2018-06-05 01:30, Baesken, Matthias wrote:
>
> Hi Erik , is there  some info available about  the performance impact 
> when  disabling  disabling speculative execution  ?
>
> And which compiler versions are needed for this ?
>
> Best regards, Matthias
>
> >We need to add compilation flags for disabling speculative execution to
>
> >our native libraries and executables. In order to allow for users not
>
> >affected by problems with speculative execution to run a JVM at full
>
> >speed, we need to be able to ship two JVM libraries - one that is
>
> >compiled with speculative execution enabled, and one that is compiled
>
> >without. Note that this applies to the build time C++ flags, not the
>
> >compiler in the JVM itself. Luckily adding these flags to the rest of
>
> >the native libraries did not have a significant performance impact so
>
> >there is no need for making it optional there.
>
> >
>
> >This patch defines flags for disabling speculative execution for GCC and
>
> >Visual Studio and applies them to all binaries except libjvm when
>
> >available in the compiler. It defines a new jvm feature
>
> >no-speculative-cti, which is used to control whether to use the flags
>
> >for libjvm. It also defines a new jvm variant "altserver" which is the
>
> >same as server, but with this new feature added.
>
> >
>
> >For Oracle builds, we are changing the default for linux-x64 and
>
> >windows-x64 to build both server and altserver, giving the choice to the
>
> >user which JVM they want to use. If others would prefer this default, we
>
> >could make it default in configure as well.
>
> >
>
> >The change in GensrcJFR.gmk fixes a newly introduced race that appears
>
> >when building multiple jvm variants.
>
> >
>
> >Bug: https://bugs.openjdk.java.net/browse/JDK-8202384
>
> >
>
> >Webrev: http://cr.openjdk.java.net/~erikj/8202384/webrev.01 
> <http://cr.openjdk.java.net/%7Eerikj/8202384/webrev.01>
>