Messages in this thread Patch in this message | | | Date | Fri, 8 Jan 2016 09:58:26 -0700 | From | Ross Zwisler <> | Subject | Re: [PATCH] x86: Micro-optimise clflush_cache_range() |
| |
On Fri, Jan 08, 2016 at 09:55:33AM +0000, Chris Wilson wrote: > 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> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: x86@kernel.org > 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: Ross Zwisler <ross.zwisler@linux.intel.com> > Cc: Sai Praneeth <sai.praneeth.prakhya@intel.com> > Cc: linux-kernel@vger.kernel.org > Acked-by: "H. Peter Anvin" <hpa@zytor.com>
Looks good to me.
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> --- > 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 a3137a4feed1..6000ad7f560c 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(); > -- > 2.7.0.rc3 >
| |