Messages in this thread Patch in this message | | | Date | Fri, 8 Jan 2016 10:30:53 -0800 | From | tip-bot for Chris Wilson <> | Subject | [tip:x86/mm] x86/mm: Micro-optimise clflush_cache_range() |
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Commit-ID: 1f1a89ac05f6e88aa341e86e57435fdbb1177c0c Gitweb: http://git.kernel.org/tip/1f1a89ac05f6e88aa341e86e57435fdbb1177c0c Author: Chris Wilson <chris@chris-wilson.co.uk> AuthorDate: Fri, 8 Jan 2016 09:55:33 +0000 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Fri, 8 Jan 2016 19:27:39 +0100
x86/mm: Micro-optimise clflush_cache_range()
Whilst inspecting the asm for clflush_cache_range() and some perf profiles that required extensive flushing of single cachelines (from part of the intel-gpu-tools GPU benchmarks), we noticed that gcc was reloading boot_cpu_data.x86_clflush_size on every iteration of the loop. We can manually hoist that read which perf regarded as taking ~25% of the function time for a single cacheline flush.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> Acked-by: "H. Peter Anvin" <hpa@zytor.com> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Borislav Petkov <bp@suse.de> Cc: Luis R. Rodriguez <mcgrof@suse.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Sai Praneeth <sai.praneeth.prakhya@intel.com> Link: http://lkml.kernel.org/r/1452246933-10890-1-git-send-email-chris@chris-wilson.co.uk Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- arch/x86/mm/pageattr.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index a3137a4..6000ad7 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -129,14 +129,16 @@ within(unsigned long addr, unsigned long start, unsigned long end) */ void clflush_cache_range(void *vaddr, unsigned int size) { - unsigned long clflush_mask = boot_cpu_data.x86_clflush_size - 1; + const unsigned long clflush_size = boot_cpu_data.x86_clflush_size; + void *p = (void *)((unsigned long)vaddr & ~(clflush_size - 1)); void *vend = vaddr + size; - void *p; + + if (p >= vend) + return; mb(); - for (p = (void *)((unsigned long)vaddr & ~clflush_mask); - p < vend; p += boot_cpu_data.x86_clflush_size) + for (; p < vend; p += clflush_size) clflushopt(p); mb();
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