Re: RCU related performance regression in 3.3

[Pascal Chapperon]

Le 04/05/2012 17:04, Paul E. McKenney a Ãcrit :
> On Fri, May 04, 2012 at 04:42:54PM +0200, Pascal Chapperon wrote:
> > Le 01/05/2012 17:45, Paul E. McKenney a Ãcrit :
> >
> > > Here is my RCU_FAST_NO_HZ patch stack on top of v3.4-rc4.
> > >
> > > Or you can pull branch fnh.2012.05.01a from:
> > >
> > > 	git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> > >
> > > 							Thanx, Paul
> > I applied your global patch on top of v3.4-rc4. But the slowdown is
> > worse than before : boot sequence took 80s instead 20-30s (12s for
> > initramfs instead of 2s).
> >
> > I'll send you rcu tracing log in a second mail.
>
> Hmmm...  Well, I guess I am glad that I finally did something that
> had an effect, but I sure wish that the effect had been in the other
> direction!
>
> Just to make sure I understand: the difference between the 20-30s and
> the 80s is exactly the patch I sent you?
>
> 							Thanx, Paul
Yes. Exactly same kernel config as in previous results, I applied your 
patch against v3.4-rc4, and sorry, the result is exactly what I said;
I saw that your global patch was quite huge, and addresses things which
are not directly related with the initial patch (commit 
7cb92499000e3c86dae653077b1465458a039ef6); maybe a side effect?

However, I'm ready to try this patch on my smaller laptop which
supports well CONFIG_FAST_NO_HZ=y and systemd, if you think it can
help ?

Another thought: this issue as nothing to do with i7 Hyper-threading
capacities ? (as I test core2duo, Pentium ulv in same conditions and I
don't encountered any slowdown ?)

Pascal

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