x86,pat Convert memtype_lock into an rw_lock.
in [Kernel]
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From: Peter Zijlstra on 24 Mar 2010 12:40 On Wed, 2010-03-24 at 09:12 -0700, Suresh Siddha wrote: > On Wed, 2010-03-24 at 04:32 -0700, Peter Zijlstra wrote: > > On Wed, 2010-03-17 at 16:19 -0800, Suresh Siddha wrote: > > > On Wed, 2010-03-17 at 12:51 -0700, H. Peter Anvin wrote: > > > > Well, as you know :) tglx and I are on the road ... I'll try to get to it on Friday before I take off again. > > > > > > Also I talked to Thomas about this rwlock conversion and he referred to > > > RT issues with rwlock. And the best is to avoid this using RCU. > > > > Its not just RT, even for mainline rwlock_t is a massive pain and often > > is no better (actually worse) than a spinlock due to the massive > > cacheline bouncing it introduces. > > Don't we have the same cacheline bouncing issues with the ticket > spinlocks? Sure, but the rwlock_t is unfair and can degrade into much worse performance than the spinlock. Thing is, rwlock_t needs to write to the cacheline for each read acquire, so unless the hold time is much-much longer than the cacheline bounce time, its just not worth it, but since its a rwlock_t it should be have short hold time, hence its a useless construct :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |