Messages in this thread | | | Date | Thu, 16 Jun 2011 17:24:04 -0700 | From | Andi Kleen <> | Subject | Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex |
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> The fact is, glibc is just total crap. > > I tried to send uli a patch to just add caching. No go. I sent > *another* patch to at least make glibc use a sane interface (and the > cache if it needs to fall back on /proc/stat for some legacy reason). > We'll see what happens.
FWIW a rerun with this modified LD_PRELOAD that does caching seems to have the same performance as the version that does sched_getaffinity.
So you're right. Caching indeed helps and my assumption that the child would only do it once was incorrect.
The only problem I see with it is that it doesn't handle CPU hotplug, but Paul's suggestion would fix that too.
> Paul Eggbert suggested "caching for one second" - by just calling > "gettimtofday()" to see how old the cache is. That would work too. >
Maybe we need a "standard LD_PRELOAD library to improve glibc" @)
-Andi
// gcc -fPIC -shared sysconf-caching.c -ldl -o sysconf-caching.so #define _GNU_SOURCE 1 #include <dlfcn.h> #include <sched.h> #include <unistd.h>
static long int (*real_sysconf)(int name);
long int sysconf(int name) { if (!real_sysconf) real_sysconf = dlsym(RTLD_NEXT, "sysconf");
if (name == _SC_NPROCESSORS_ONLN) { static int cache = -1;
if (cache == -1) cache = real_sysconf( _SC_NPROCESSORS_ONLN); return cache; }
return real_sysconf(name); }
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