Re: RCU related performance regression in 3.3

[Pascal Chapperon]

Le 18/04/2012 17:23, Paul E. McKenney a Ãcrit :
> > systemd is controlling the whole boot process including mount
> > operation (apart root filesystem) and as I can see, uses heavily
> > sockets to do it (not to mention cpu-affinity). It controls also the
> > major part of umount operations. Is it possible that your patch hits
> > a systemd bug ?
>
> Is it possible that systemd is using network operations that include
> synchronize_rcu()?  Then if you did the same operation from the
> command line at runtime, you might not see the slowdown.
>
> Is it possible for you to convince systemd to collect RCU event tracing
> during the slow operation?  RCU event tracing is available under
> /sys/kernel/debug/tracing/rcu.
-
Paul, thank you for these suggestions : I'll manage to enable RCU event
tracing immediately after mounting debugfs (systemd permits custom
units). As debugfs is mounted early in the boot sequence, maybe I'll
catch something.

Pascal

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