From e35735b9a5d8d38d9ffe2f1f0cdcbb0d45c42eff Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Thu, 2 Oct 2014 15:44:21 +1000 Subject: [PATCH] powerpc: Speed up clear_page by unrolling it Unroll clear_page 8 times. A simple microbenchmark which allocates and frees a zeroed page: for (i = 0; i < iterations; i++) { unsigned long p = __get_free_page(GFP_KERNEL | __GFP_ZERO); free_page(p); } improves 20% on POWER8. This assumes cacheline sizes won't grow beyond 512 bytes or page sizes wont drop below 1kB, which is unlikely, but we could add a runtime check during early init if it makes people nervous. Michael found that some versions of gcc produce quite bad code (all multiplies), so we give gcc a hand by using shifts and adds. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- Reading git-format-patch failed