On Fri, Apr 06, 2012 at 11:18:03AM +0200, Pascal Chapperon wrote:RCU_IDLE_GP_DELAY=3 instead of 6 does not improve significantlyMessage du 05/04/12 16:40A full kernel compilation (make -j 16) takes 14mn with both 3.2.10 and 3.3.0.
De : "Paul E. McKenney"
A : "Pascal CHAPPERON"
Copie à : "Josh Boyer" , linux-kernel@xxxxxxxxxxxxxxx, kernel-team@xxxxxxxxxxxxxxxxx
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.
OK, good.
OK, so the natural approach is to disable CONFIG_RCU_FAST_NO_HZ atIn fact, I need it to remain disable until all the systemd units are completed.
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.
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.
OK...
If RCU has some way to find out when init is complete, I can easilyI said that I didn't noticed significant slowdown during runtime, but my
make it so that CONFIG_RCU_FAST_NO_HZ optimizes for speed during boot
and energy efficiency during runtime.
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 to try first -- could you please check boot/shutdown slowdown
with the patch below?
But yes, there are things like modifying netfilter rules and updating
security configuration that might be affected.
One thing I could easily do would be to provide a sysfs parameter orSo the feature is disabled until you trigger a sysfs parameter, and can be
some such that allows the boot process to enable energy-efficiency
mode at runtime. I would much prefer to make this automatic, though.
disabled before shutdown ? It would be fair, at least for hardware like my
own.
That is the thought, though again I would really really prefer that this
be automated.
Other thoughts?Do you think that the culprit is a buggy hardware in my laptop, or the
number of cpu/threads ?
Maybe just more filesystems to mount?
Thanx, Paul
Resent in plain text because rejected. Sorry, i forgot the rules.
No problem! Please see below for the patch.
Thanx, Paul