Messages in this thread | | | Date | Wed, 18 Jun 2014 11:31:04 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v2 1/2] mm, thp: move invariant bug check out of loop in __split_huge_page_map |
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On 06/18/2014 08:24 AM, Kirill A. Shutemov wrote: > On Tue, Jun 17, 2014 at 06:37:58PM -0400, Waiman Long wrote: >> In the __split_huge_page_map() function, the check for >> page_mapcount(page) is invariant within the for loop. Because of the >> fact that the macro is implemented using atomic_read(), the redundant >> check cannot be optimized away by the compiler leading to unnecessary >> read to the page structure. >> >> This patch moves the invariant bug check out of the loop so that it >> will be done only once. On a 3.16-rc1 based kernel, the execution >> time of a microbenchmark that broke up 1000 transparent huge pages >> using munmap() had an execution time of 38,245us and 38,548us with >> and without the patch respectively. The performance gain is about 1%. > For this low difference it would be nice to average over few runs + > stddev. It can easily can be a noise.
The timing data was the average of 5 runs with a SD of 100-200us. >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> > But okay: > > Acked-by: Kirill A. Shutemov<kirill.shutemov@linux.intel.com> >
Thank for the review.
-Longman
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