Commit 1f1a89ac authored Jan 08, 2016 by Chris Wilson Committed by Thomas Gleixner Jan 08, 2016

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>

parent 2039e6ac

arch/x86/mm/pageattr.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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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