Messages in this thread | | | Date | Tue, 5 Dec 2017 15:49:48 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] list_lru: Prefetch neighboring list entries before acquiring lock |
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On Wed 29-11-17 09:17:34, Waiman Long wrote: > The list_lru_del() function removes the given item from the LRU list. > The operation looks simple, but it involves writing into the cachelines > of the two neighboring list entries in order to get the deletion done. > That can take a while if the cachelines aren't there yet, thus > prolonging the lock hold time. > > To reduce the lock hold time, the cachelines of the two neighboring > list entries are now prefetched before acquiring the list_lru_node's > lock. > > Using a multi-threaded test program that created a large number > of dentries and then killed them, the execution time was reduced > from 38.5s to 36.6s after applying the patch on a 2-socket 36-core > 72-thread x86-64 system. > > Signed-off-by: Waiman Long <longman@redhat.com>
The patch still seems to be in the mmotm tree while it breaks compilation. At least m32r defconfig complains with mm/list_lru.c: In function 'list_lru_del': mm/list_lru.c:141:2: error: implicit declaration of function 'prefetchw' [-Werror=implicit-function-declaration] prefetchw(item->prev);
It also seems that there is no general agreement in the patch. Andrew, do you plan to keep it? -- Michal Hocko SUSE Labs
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