Messages in this thread | | | Date | Fri, 6 Apr 2012 11:18:03 +0200 (CEST) | From | Pascal Chapperon <> | Subject | Re: RCU related performance regression in 3.3 |
| |
> Message du 05/04/12 16:40 > De : "Paul E. McKenney" > A : "Pascal CHAPPERON" > Copie à : "Josh Boyer" , linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org > Objet : Re: RCU related performance regression in 3.3 > > On Thu, Apr 05, 2012 at 04:15:33PM +0200, Pascal CHAPPERON wrote: > > Hello, > > > > I didn't notice any significant slowdown while the system is up and running. A full kernel compilation (make -j 16) takes 14mn with both 3.2.10 and 3.3.0. > > OK, so the natural approach is to disable CONFIG_RCU_FAST_NO_HZ at > boot time. Unfortunately, you appear to need it to remain disabled > through at least filesystem mounting, which if I understand correctly > happens long after system_state gets set to SYSTEM_RUNNING. > In fact, I need it to remain disable until all the systemd units are completed. Some units, such as NetworkManager can take longer time to complete with RCU_FAST_NO_HZ enabled. And i need it to be disabled at shutdown, as umounting cgroups, sysfs, etc. plus old-root mounting can take one plain second for each umounting.
> If RCU has some way to find out when init is complete, I can easily > make it so that CONFIG_RCU_FAST_NO_HZ optimizes for speed during boot > and energy efficiency during runtime. > I said that I didn't noticed significant slowdown during runtime, but my laptop usage is basic. Some specific tasks similar to systemd may perhaps be impacted by this feature. I can test a task/program that could stress RCU_FAST_NO_HZ if any ?
> One thing I could easily do would be to provide a sysfs parameter or > some such that allows the boot process to enable energy-efficiency > mode at runtime. I would much prefer to make this automatic, though. > So the feature is disabled until you trigger a sysfs parameter, and can be disabled before shutdown ? It would be fair, at least for hardware like my own.
> Other thoughts? > Do you think that the culprit is a buggy hardware in my laptop, or the number of cpu/threads ?
> Thanx, Paul >
Resent in plain text because rejected. Sorry, i forgot the rules.
Pascal -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |