Messages in this thread |  | | | Date | Sun, 18 Sep 2005 18:08:35 +1000 | | From | Nick Piggin <> | | Subject | Re: [PATCH 2/5] atomic: introduce atomic_inc_not_zero |
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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.
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