Messages in this thread |  | | Date | Tue, 4 Feb 2020 13:47:59 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 7/7] locking/lockdep: Add a fast path for chain_hlocks allocation |
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On Mon, Feb 03, 2020 at 11:41:47AM -0500, Waiman Long wrote: > When alloc_chain_hlocks() is called, the most likely scenario is > to allocate from the primordial chain block which holds the whole > chain_hlocks[] array initially. It is the primordial chain block if its > size is bigger than MAX_LOCK_DEPTH. As long as the number of entries left > after splitting is still bigger than MAX_CHAIN_BUCKETS it will remain > in bucket 0. By splitting out a sub-block at the end, we only need to > adjust the size without changing any of the existing linkage information. > This optimized fast path can reduce the latency of allocation requests. > > This patch does change the order by which chain_hlocks entries are > allocated. The original code allocates entries from the beginning of > the array. Now it will be allocated from the end of the array backward.
Cute; but why do we care? Is there any measurable performance indicator?
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