linux-kernel - Re: [rfc][patch 2/2] x86

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Date:	Mon, 16 Jul 2007 11:49:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andi Kleen <ak@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc][patch 2/2] x86_64: FIFO ticket spinlocks


* Nick Piggin <npiggin@...e.de> wrote:

> On Mon, Jul 16, 2007 at 11:26:46AM +0200, Ingo Molnar wrote:
> > 
> > * Nick Piggin <npiggin@...e.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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