Messages in this thread | | | Date | Wed, 18 Jun 2014 15:24:42 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2 1/2] mm, thp: move invariant bug check out of loop in __split_huge_page_map |
| |
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.
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
But okay:
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
-- Kirill A. Shutemov
| |