* Changli Gao (xiaosuo@xxxxxxxxx) wrote: > On Tue, Aug 17, 2010 at 5:01 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > > > > I am not sure we must use a long (we really need 4 bytes only), and last > > time I tried to use cmpxchg(), I was being told it was not available on > > all arches. > > > > But seeing it used in kernel/pid.c, maybe its not true anymore (that is, > > __HAVE_ARCH_CMPXCHG is always defined to 1) > > > > Since its a recent change (in kernel/pid.c), I would wait a bit and see > > if an arch maintainer complains ;) > > > > > > I searched the code, and found ext4, btrfs, lockdep, perf and trace > all use cmpxchg(). And after this patch serial > (http://linux.derkeiler.com/Mailing-Lists/Kernel/2007-08/msg05032.html) > was merged, maybe cmpxchg() is generic. Is there an SMP processor > doesn't support cmpxchg()? I made sure it was available on all architectures with that patchset, with the intended goal to used it (cmpxchg, cmpxchg_local for 32/64-bit and cmpxchg64, cmpxchg64_local for 64-bit) in arch-agnostic tracer code. I added a cmpxchg emulated with irqs off for uniprocessor-only architectures that did not have CAS support. sparc32 has moved to a hashed locked scheme for its atomic operations long ago, which makes the full 32 bits available. So, all in all, I'd be surprised if an architecture would lack cmpxchg() today. It might be possible that a new architecture that just came in would not have taken care of deploying cmpxchg, but that should be easily fixable. Please see Documentation/atomic_ops.txt for details. Thanks, Mathieu > > -- > Regards, > Changli Gao(xiaosuo@xxxxxxxxx) -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
