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x86/mm: Micro-optimise clflush_cache_range()

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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>
This commit is contained in:
Chris Wilson 2016-01-08 09:55:33 +00:00 committed by Thomas Gleixner
parent 2039e6acaf
commit 1f1a89ac05
1 changed files with 6 additions and 4 deletions
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10
arch/x86/mm/pageattr.c
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@ -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();