Messages in this thread | | | Date | Mon, 11 Jul 2016 13:37:41 -0400 | From | Waiman Long <> | Subject | Re: [RESEND PATCH 1/5] lib/dlock-list: Distributed and lock-protected lists |
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On 06/07/2016 04:13 PM, Andi Kleen wrote: > On Tue, Jun 07, 2016 at 03:35:51PM -0400, Waiman Long wrote: >> Linked list is used everywhere in the Linux kernel. However, if many >> threads are trying to add or delete entries into the same linked list, >> it can create a performance bottleneck. >> >> This patch introduces a new list APIs that provide a set of distributed >> lists (one per CPU), each of which is protected by its own spinlock. > One thing I don't like is that it is per CPU. One per CPU is almost > certainly overkill and not needed for true scalability, especially > on systems using SMT. Also it makes the case where everything has to > be walked more and more expensive, because all these locks have to > be taken. Even when not contended this will add up.
When iterating the lists, the lock shouldn't be taken when a list is empty.
> It would be better to do this per every Nth CPU. Now I don't have > a clear answer what the best N is, but I'm pretty sure it's> 1. > For example at least on SMT systems only per core instead of per > thread. Likely even more coarse grained, although per socket > may be not good enough. > > -Andi
I have just sent out an updated patch to mapped 2 cores to each list. Maybe you can take a look to see if that is good enough from your point of view.
Cheers, Longman
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