Messages in this thread | | | Date | Wed, 23 Apr 2008 13:54:31 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH 11/11] s390: convert to generic helpers for IPI function calls |
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On Wed, Apr 23 2008, Heiko Carstens wrote: > > > > Your generic patch changes semantics of smp_call_function(). At least the > > > > s390 version of smp_call_function() mask used to not return unless all IPIs > > > > where received on the target cpus. > > > > Your patch changes that. It will already return as soon as all IPIs have > > > > been sent. Unfortunately Martin's etr code in arch/s390/kernel/time.c > > > > > > Yep, this is what I mentioned in the intro mail. > > > > > > > relies on exactly the old semantics. > > > > > > OK, I could not see anything which relied on that and I did think that > > > it was a somewhat odd interface. By the time that smp_call_function() > > > stops waiting for startups, we could easily be in the condition that the > > > N-1 CPUs executed the function part a long time ago. I just didn't see > > > much usefulness in that, you may as well just set wait == 1 in that > > > case. > > > > > > > Since this seems to be an s390 only issue, could you just drop the s390 > > > > conversion patch? We'll have to think about how to change the err code > > > > and convert later I guess. > > > > > > I'll drop the s390 bits. I can easily add something like > > > smp_call_function_foo() that has this behaviour. > > > > I added an smp_call_function_sync() for this purpose and kept the s390 > > conversion, I would very much appreciate if you could look it over. I > > wont post the full patchset again today, but you can inspect it here: > > > > http://git.kernel.dk/?p=linux-2.6-block.git;a=shortlog;h=refs/heads/generic-ipi > > > > The interesting bits are patch #1 for the generic bits and patch #11 for > > the s390 part. Thanks! > > I don't think that works: the old code also relied on the fact that there > could be only one cpu sending an smp_call_* IPI (serialized by call_lock). > The current etr code exploits that to serialize all cpus: > > Do smp_call_function() to force all other cpus into clock_sync_cpu_start() > where they sort of busy wait(!). Then the master cpu is syncing the clock > and when it finished the other cpus may continue again and finally leave > the smp_call_function interrupt handler. > > Your patch series however doesn't make sure anymore that there is only > one cpu doing an smp_call_function*, so we may deadlock as soon as two > cpus are trying to synchronize all cpus this way. > After all I think the etr code should be converted to use stop_machine_run > instead. However that doesn't allow for master/slave cpus.
You are right. I'll drop the code again, it would be nice to get rid of this interface, I guess s390 can do that when they convert to the generic helpers.
-- Jens Axboe
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