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Date: Fri, 22 Aug 2008 11:47:39 +1000 From: Nick Piggin <nickpiggin@...oo.com.au> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>, "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>, Suresh Siddha <suresh.b.siddha@...el.com>, Jens Axboe <jens.axboe@...cle.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Rusty Russell <rusty@...tcorp.com.au> Subject: Re: [PATCH 1/2] smp_call_function: don't use lock in call_function_data On Friday 22 August 2008 10:29, Jeremy Fitzhardinge wrote: > There's no need for a lock in call_function_data, since it's only used > to decrement-and-test a counter. Use an atomic instead. Actually I wanted to convert the cpu_clear operation to be non-atomic, and keep it under the lock. Thus the spinlock would save one atomic operation. I simply forgot about this after Jens took over the patchset. We could get rid of that WARN_ON branch in 2.6.28 I expect, unless we see it trigger. > > Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com> > --- > kernel/smp.c | 17 ++++------------- > 1 file changed, 4 insertions(+), 13 deletions(-) > > =================================================================== > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -10,6 +10,7 @@ > #include <linux/rcupdate.h> > #include <linux/rculist.h> > #include <linux/smp.h> > +#include <asm/atomic.h> > > bool __read_mostly smp_single_ipi_queue = false; > > @@ -37,8 +38,7 @@ > > struct call_function_data { > struct call_single_data csd; > - spinlock_t lock; > - unsigned int refs; > + atomic_t refs; > cpumask_t cpumask; > struct rcu_head rcu_head; > }; > @@ -125,21 +125,13 @@ > */ > rcu_read_lock(); > list_for_each_entry_rcu(data, &queue->list, csd.list) { > - int refs; > - > if (!cpu_isset(cpu, data->cpumask)) > continue; > > data->csd.func(data->csd.info); > > - spin_lock(&data->lock); > cpu_clear(cpu, data->cpumask); > - WARN_ON(data->refs == 0); > - data->refs--; > - refs = data->refs; > - spin_unlock(&data->lock); > - > - if (refs) > + if (!atomic_dec_and_test(&data->refs)) > continue; > > spin_lock(&queue->lock); > @@ -379,10 +371,9 @@ > slowpath = 1; > } > > - spin_lock_init(&data->lock); > data->csd.func = func; > data->csd.info = info; > - data->refs = num_cpus; > + atomic_set(&data->refs, num_cpus); > data->cpumask = mask; > > spin_lock_irqsave(&queue->lock, flags); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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