Messages in this thread | | | Date | Mon, 16 Jul 2007 12:18:28 +0200 | From | Nick Piggin <> | Subject | Re: [rfc][patch 2/2] x86_64: FIFO ticket spinlocks |
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On Mon, Jul 16, 2007 at 11:49:40AM +0200, Ingo Molnar wrote: > > * Nick Piggin <npiggin@suse.de> wrote: > > > On Mon, Jul 16, 2007 at 11:26:46AM +0200, Ingo Molnar wrote: > > > > > > * Nick Piggin <npiggin@suse.de> wrote: > > > > > > > [...] trylock is more significantly slower, but they are relatively > > > > rare. > > > > > > trylock is the main thing that the spinlock debugging code uses, and > > > SPINLOCK_DEBUG is frequently enabled by distro kernels. OTOH, the cost > > > looks like to be +5 instructions, right? Still ... > > > > Which trylocks do you mean? The lockbreak spinlocks use trylock, but > > those are not used with the ticket version. > > the trylocks in lib/spinlock-debug.c: > > static void __spin_lock_debug(spinlock_t *lock) > { > ... > if (__raw_spin_trylock(&lock->raw_lock)) > return; > ... > void _raw_spin_lock(spinlock_t *lock) > { > debug_spin_lock_before(lock); > if (unlikely(!__raw_spin_trylock(&lock->raw_lock))) > __spin_lock_debug(lock); > debug_spin_lock_after(lock); > } > > am i missing something?
No, I missed that. Yeah, that would get a bit slower, but I'm not sure if it would be a problem on a kernel where you have spinlock debuggin on anyway.
If it becomes a problem, we could perhaps do a version for ticket locks that first takes a ticket, and then is for up to a second before printing the stuck lock message. That would make the performance hit go away.
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