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SubjectRe: [rfc][patch 2/2] x86_64: FIFO ticket spinlocks

* 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?

Ingo
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