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selinux: de-crapify avc cache stat code generation 

You can turn off the avc cache stats, but distributions seem to not do
that (perhaps because several performance tuning how-to's talk about the
avc cache statistics).

Which is sad, because the code it generates is truly horrendous, with
the statistics update being sandwitched between get_cpu/put_cpu which in
turn causes preemption disables etc.  We're talking ten+ instructions
just to increment a per-cpu variable in some pretty hot code.

Fix the craziness by just using 'this_cpu_inc()' instead.  Suddenly we
only need a single 'inc' instruction to increment the statistics.  This
is quite noticeable in the incredibly hot avc_has_perm_noaudit()
function (which triggers all the statistics by virtue of doing an
avc_lookup() call).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2011-05-19 18:59:47 -07:00
parent 39ab05c8e0
commit 044aea9b83
1 changed files with 1 additions and 5 deletions
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6
security/selinux/avc.c
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@ -38,11 +38,7 @@
#define AVC_CACHE_RECLAIM 16 #define AVC_CACHE_RECLAIM 16
#ifdef CONFIG_SECURITY_SELINUX_AVC_STATS #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
#define avc_cache_stats_incr(field) \ #define avc_cache_stats_incr(field) this_cpu_inc(avc_cache_stats.field)
do { \
per_cpu(avc_cache_stats, get_cpu()).field++; \
put_cpu(); \
} while (0)
#else #else
#define avc_cache_stats_incr(field) do {} while (0) #define avc_cache_stats_incr(field) do {} while (0)
#endif #endif