Re: [RFC][PATCH 12/13] stop_machine: Remove lglock

From: Peter Zijlstra
Date: Tue Jun 23 2015 - 07:21:02 EST

On Tue, Jun 23, 2015 at 12:55:48PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 23, 2015 at 12:09:32PM +0200, Peter Zijlstra wrote:
> > We can of course slap a percpu-rwsem in, but I wonder if there's
> > anything smarter we can do here.
> Urgh, we cannot use percpu-rwsem here, because that would require
> percpu_down_write_trylock(), and I'm not sure we can get around the
> sync_sched() for that.
> Now try_stop_cpus(), which requires the down_write_trylock() is used to
> implement synchronize_sched_expedited().
> Using sync_sched() to implement sync_sched_expedited would make me
> happy, but it does somewhat defeat the purpose.

Paul, why does this use stop_machine anyway? I seemed to remember you
sending resched IPIs around.

The rcu_sched_qs() thing would set passed_quiesce, which you can then
collect to gauge progress.

Shooting IPIs around is bad enough, but running a full blown
stop_machine is really blunt and heavy.

Also, OMFG @ 74b51ee152b6 ("ACPI / osl: speedup grace period in
acpi_os_map_cleanup"), that's an expedited use to help the nVidiot
binary blob. WTF!!

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at