Messages in this thread | | | Date | Mon, 17 Mar 2008 20:53:01 +0100 | From | Jens Axboe <> | Subject | Re: [Patch (block.git) 2/2] Ensure single IPI generation for SMP call single |
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On Mon, Mar 17 2008, Jens Axboe wrote: > On Mon, Mar 17 2008, Alan D. Brunelle wrote: > > diff --git a/kernel/smp.c b/kernel/smp.c > > index 7232e1c..f7ec401 100644 > > --- a/kernel/smp.c > > +++ b/kernel/smp.c > > @@ -23,28 +23,34 @@ void __cpuinit generic_init_call_single_data(void) > > > > void generic_smp_call_function_single_interrupt(void) > > { > > - struct call_single_queue *q; > > unsigned long flags; > > LIST_HEAD(list); > > + struct call_single_queue *q = &__get_cpu_var(call_single_queue); > > > > - q = &__get_cpu_var(call_single_queue); > > spin_lock_irqsave(&q->lock, flags); > > - list_replace_init(&q->list, &list); > > - spin_unlock_irqrestore(&q->lock, flags); > > + while (!list_empty(&q->list)) { > > + list_replace_init(&q->list, &list); > > + spin_unlock_irqrestore(&q->lock, flags); > > > > - while (!list_empty(&list)) { > > - struct call_single_data *data; > > + do { > > + struct call_single_data *data; > > > > - data = list_entry(list.next, struct call_single_data, list); > > - list_del(&data->list); > > + data = list_entry(list.next, struct call_single_data, > > + list); > > + list_del(&data->list); > > > > - data->func(data->info); > > - if (data->flags & CSD_FLAG_WAIT) { > > - smp_wmb(); > > - data->flags = 0; > > - } else if (data->flags & CSD_FLAG_ALLOC) > > - kfree(data); > > + data->func(data->info); > > + if (data->flags & CSD_FLAG_WAIT) { > > + smp_wmb(); > > + data->flags = 0; > > + } else if (data->flags & CSD_FLAG_ALLOC) > > + kfree(data); > > + } while (!list_empty(&list)); > > + > > + spin_lock_irqsave(&q->lock, flags); > > } > > + q->activated = 0; > > + spin_unlock_irqrestore(&q->lock, flags); > > } > > I agree with doing it this way, re-checking and doing another run (or > more). However I think we can improve it a bit so we don't always have > to grab the dst lock at least twice - it should be safe enough to > include the lock only inside the first loop, doing an smp_mb() before > the list_empty() check and again at the bottom before looping around and > doing the list_empty() check again. > > I've rolled a new patch series here: > > http://git.kernel.dk/?p=linux-2.6-block.git;a=shortlog;h=io-cpu-affinity > > (or just pull the io-cpu-affinity branch), it also includes a bunch of > other cleanups like porting the faster smp_call_function() to ia64 and > powerpc as well. So the kernel/smp.c generic helpers have grown a bit, > while the arch bits are smaller. > > I'm curious if it now boots on ia64, since I killed the hack to manually > call the __init manually there. If you could check, I would appreciate > it ;-) > > I've built all 4 supported archs and they compile and link fine, but > nothing has been booted yet.
x86 and x86-64 boot just fine, so powerpc should work as well (will do performance testing on a 4-way ppc tomorrow). ia64 should also work, as long as the init_call_single_data() gets called correctly.
If it doesn't work on tha ia64, try and change the core_initcall() to a postcore_initcall() or even an arch_initcall(). It now resides in kernel/smp.c.
-- Jens Axboe
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