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Roman Zippel wrote: > Hi, > > On Thu, 15 Sep 2005, Nick Piggin wrote: > > >>Roman: any ideas about what you would prefer? You'll notice >>atomic_inc_not_zero replaces rcuref_inc_lf, which is used several times >>in the VFS. > > > In the larger picture I'm not completely happy with these scalibilty > patches, as they add extra overhead at the lower end. On a UP system in > general nothing beats: > > spin_lock(); > if (*ptr) > ptr += 1; > spin_unlock(); > > The main problem is here that the atomic functions are used in two basic > situation: > > 1) interrupt synchronization > 2) multiprocessor synchronization > > The atomic functions have to assume both, but on UP systems it often is > a lot cheaper if they don't have to synchronize with interrupts. So > replacing a spinlock with a few atomic operations can hurt UP performance. > Maybe so, but what I'm doing is introducing a slightly better implementation of what is currently in tree, and attempting to follow current standards as far as possible. I don't think you could say that is a bad thing. Now I don't think anyone would be flat out opposed to 1 - reworking the atomic.h code to allow some genericity (is that a word?); 2 - reworking atomic.h code to allow combining of atomic ops, or allowing interrupt unsafe ops... Of course, neither is going to be merged unless done tastefully, and I imagine both would be difficult to get right, with probably a low cost/benefit ratio. Thanks, Nick -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||
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