Messages in this thread | | | Date | Mon, 1 Jul 2013 14:50:46 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64 |
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* Borislav Petkov <bp@alien8.de> wrote:
> On Mon, Jul 01, 2013 at 01:11:22PM +0200, Ingo Molnar wrote: > > Hm, a 6 seconds win looks _way_ too much - we don't execute that much > > mutex code, let alone a portion of it. > > > > This could perhaps be a bootup-to-bootup cache layout systematic jitter > > artifact, which isn't captured by stddev observations? > > > > Doing something like this with a relatively fresh version of perf: > > > > perf stat --repeat 10 -a --sync \ > > --pre 'make -s O=defconfig-build/ clean; echo 1 > /proc/sys/vm/drop_caches' \ > > make -s -j64 O=defconfig-build/ bzImage > > > > ... might do the trick (untested!). (Also note the use of -a: this should > > run on an otherwise quiescent system.) > > Yep, I didn't run -a since I wanted to trace only the build process. > Btw, the build-kernel.sh script looks like this: > > #!/bin/bash > > NUM_CPUS=$(cat /proc/cpuinfo | grep processor | wc -l) > MAKE_OPTS=-j$(($NUM_CPUS+1)) > > echo 3 > /proc/sys/vm/drop_caches > make $MAKE_OPTS mrproper > make $MAKE_OPTS oldconfig > make $MAKE_OPTS > <EOF> > > Let me try your perf tracing variant. > > > As a sidenote, we could add this as a convenience feature, triggered via: > > > > perf stat --flush-vm-caches > > > > ... or so, in addition to the already existing --sync option. > > Is this something which we want to use a lot? [...]
For cache-cold measurements I'm sure it's handy.
> [...] Also, there's 1, 2 and 3 as arg to drop_caches: > > drop_caches > > Writing to this will cause the kernel to drop clean caches, dentries and > inodes from memory, causing that memory to become free. > > To free pagecache: > echo 1 > /proc/sys/vm/drop_caches > To free dentries and inodes: > echo 2 > /proc/sys/vm/drop_caches > To free pagecache, dentries and inodes: > echo 3 > /proc/sys/vm/drop_caches
Yeah, so it would have to be a --vm-drop-caches <N> option I guess.
Thanks,
Ingo
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