On Wed, 2010-11-17 at 02:04 +0800, Peter Zijlstra wrote: > On Tue, 2010-11-16 at 08:38 -0800, Linus Torvalds wrote: > > > > I kind of like the lock-less list implementation (it could easily be > > useful for random things, and it's very simple). > > Yes, there's various implementations floating around, and we already > have one in-kernel ( net/rds/xlist.h ), mason and axboe and me have been > kicking around various patches using that thing in other circumstances > as well. > > [ At some point we had perf -- what now is kernel/irq_work.c -- using > it as well, but the new code grew too complex due to requirements > from Huang ] I think it should be possible for them to use the general lockless list implementation in the patch. I think this will reduce some code duplication/complexity. Do you agree? > > And I don't think the > > notion of a lockless memory allocator is wrong either, although it > > looks a lot more specialized than the list thing (the solution to > > lockless allocations is generally simply to do them ahead of time). > > > Right, I don't generally object to lockless things, but they either need > to be 1) faster than the existing code, and/or 2) have a very convincing > use-case (other than performance) for their added complexity. I will post a generic hardware error reporting mechanism patchset soon. The lock-less memory allocator is used there. And I think maybe we can use it in lockdep code too. Which needs to allocate something locklessly if my understanding is correct. > Afaict the proposed patch adds lots more LOCK'ed instructions into that > allocator path than it removes, ie its a slow down for existing users. Let's take a look at gen_pool_alloc The locks removed: - one rwlock: pool->lock - one spinlock for each chunk: chunk->lock The LOCK'ed instructions added: - one or two cmpxchg in most cases. But if there is heavy contention between users, there will be more cmpxchg. So I suggest to use one gen_pool for each CPU for heavy contention situation. BTW: The original gen_pool is designed to deal with special purpose memory in some drivers. So I don't think performance is a big issue for it. Best Regards, Huang Ying -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
