|From:||Heiko Carstens <heiko.carstens-AT-de.ibm.com>|
|To:||Tejun Heo <tj-AT-kernel.org>|
|Subject:||Re: [PATCH 2/4] stop_machine: reimplement using cpuhog|
|Date:||Mon, 8 Mar 2010 18:10:20 +0100|
|Cc:||linux-kernel-AT-vger.kernel.org, rusty-AT-rustcorp.com.au, sivanich-AT-sgi.com, torvalds-AT-linux-foundation.org, mingo-AT-elte.hu, peterz-AT-infradead.org, dipankar-AT-in.ibm.com, josh-AT-freedesktop.org, paulmck-AT-linux.vnet.ibm.com, oleg-AT-redhat.com, akpm-AT-linux-foundation.org, Martin Schwidefsky <schwidefsky-AT-de.ibm.com>|
On Tue, Mar 09, 2010 at 12:53:21AM +0900, Tejun Heo wrote: > Reimplement stop_machine using cpuhog. As cpuhogs are guaranteed to > be available for all online cpus, stop_machine_create/destroy() are no > longer necessary and removed. > > With resource management and synchronization handled by cpuhog, the > new implementation is much simpler. Asking the cpuhog to execute the > stop_cpu() state machine on all online cpus with cpu hotplug disabled > is enough. > > stop_machine itself doesn't need to manage any global resources > anymore, so all per-instance information is rolled into struct > stop_machine_data and the mutex and all static data variables are > removed. > > The previous implementation created and destroyed RT workqueues as > necessary which made stop_machine() calls highly expensive on very > large machines. According to Dimitri Sivanich, preventing the dynamic > creation/destruction makes booting faster more than twice on very > large machines. cpuhog resources are preallocated for all online cpus > and should have the same effect. > > Signed-off-by: Tejun Heo <firstname.lastname@example.org> > Cc: Rusty Russell <email@example.com> > Cc: Oleg Nesterov <firstname.lastname@example.org> > Cc: Dimitri Sivanich <email@example.com> > --- > arch/s390/kernel/time.c | 1 - > drivers/xen/manage.c | 14 +--- > include/linux/stop_machine.h | 20 ----- > kernel/cpu.c | 8 -- > kernel/module.c | 14 +--- > kernel/stop_machine.c | 162 ++++++++++-------------------------------- > 6 files changed, 42 insertions(+), 177 deletions(-) > > diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c > index 65065ac..afe429e 100644 > --- a/arch/s390/kernel/time.c > +++ b/arch/s390/kernel/time.c > @@ -397,7 +397,6 @@ static void __init time_init_wq(void) > if (time_sync_wq) > return; > time_sync_wq = create_singlethread_workqueue("timesync"); > - stop_machine_create(); > } > > /* The reason we introduced stop_machine_create/destroy was to have a non-failing variant that doesn't rely on I/O. If we ever see a timesync machine check no I/O will succeed (it blocks) until clocks have been synchronized. That means also that we rely on the non-blocking semantics that those functions must have that are called via stop_machine. This isn't true anymore with the cpu hog infrastructure: if passed a blocking function that could wait on I/O we won't see any progress anymore and the machine is dead.
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