Ubuntu
glibc package

  1. Bug #1563784
  2. Comment #6

Comment 6 for bug 1563784

Revision history for this message
bugproxy (bugproxy) wrote : Comment bridged from LTC Bugzilla

------- Comment From <email address hidden> 2016-04-11 04:25 EDT-------
(In reply to comment #9)
> lock elision is enabled by default on s390x, ppc64el, amd64 on Ubuntu.

Are there any performance measurements available you could share with us regarding this? According to our measurements lock elision was not able to prove being faster in any benchmark or application we tried. We have seen some regressions with it though. I really think such a decision should only be made based on measurements. Everything positive about lock elision I've seen so far were theoretical things which failed hitting real world examples. If it really would be an overall win we would just have made it the default in Glibc.

> This is inline with other distributions too, e.g. fedora and opensuse both
> build with lock elision enabled by default.
>
> http://s390.koji.fedoraproject.org/kojifiles/packages/glibc/2.23.90/2.fc25/
> data/logs/s390x/build.log

Be aware that on Fedora lock elision is currently *only* enabled for S/390 and we already requested removing it. To our knowledge lock elision also on x86 was not able to show any benefits yet. While the Fedora guys turned it off for x86 due to the hardware bug they also mentioned that it will stay disabled until a x86 will show any benefits with it. I would prefer the very same for S/390 as well.

> https://build.opensuse.org/package/live_build_log/openSUSE:Factory:zSystems/
> glibc/standard/s390x

OpenSUSE probably just followed the Fedora example as well.

> Disabling lock elision at this point of release cycle could only be
> realistic driven by publicly known hardware issues of shipped zEC12 or later
> z Systems. Are there any publicly disclosed hardware issues with TX that
> release team needs to be aware of?

No, there are no known hardware issues with the TX implementation.

The only concern we have is that we know there are certain performance regressions without real wins. This might make the Ubuntu release look bad performance-wise in some situations when comparing against the other z enterprise distros.