Messages in this thread | | | Date | Mon, 08 Jul 2013 10:09:33 -0400 | From | Stephen Smalley <> | Subject | Re: [PATCH 1/2 v5] SELinux: Reduce overhead of mls_level_isvalid() function call |
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On 07/05/2013 01:10 PM, Waiman Long wrote: > On 06/11/2013 07:49 AM, Stephen Smalley wrote: >> On 06/10/2013 01:55 PM, Waiman Long wrote: >>> v4->v5: >>> - Fix scripts/checkpatch.pl warning. >>> >>> v3->v4: >>> - Merge the 2 separate while loops in ebitmap_contains() into >>> a single one. >>> >>> v2->v3: >>> - Remove unused local variables i, node from mls_level_isvalid(). >>> >>> v1->v2: >>> - Move the new ebitmap comparison logic from mls_level_isvalid() >>> into the ebitmap_contains() helper function. >>> - Rerun perf and performance tests on the latest v3.10-rc4 kernel. >>> >>> While running the high_systime workload of the AIM7 benchmark on >>> a 2-socket 12-core Westmere x86-64 machine running 3.10-rc4 kernel >>> (with HT on), it was found that a pretty sizable amount of time was >>> spent in the SELinux code. Below was the perf trace of the "perf >>> record -a -s" of a test run at 1500 users: >>> >>> 5.04% ls [kernel.kallsyms] [k] ebitmap_get_bit >>> 1.96% ls [kernel.kallsyms] [k] mls_level_isvalid >>> 1.95% ls [kernel.kallsyms] [k] find_next_bit >>> >>> The ebitmap_get_bit() was the hottest function in the perf-report >>> output. Both the ebitmap_get_bit() and find_next_bit() functions >>> were, in fact, called by mls_level_isvalid(). As a result, the >>> mls_level_isvalid() call consumed 8.95% of the total CPU time of >>> all the 24 virtual CPUs which is quite a lot. The majority of the >>> mls_level_isvalid() function invocations come from the socket creation >>> system call. >>> >>> Looking at the mls_level_isvalid() function, it is checking to see >>> if all the bits set in one of the ebitmap structure are also set in >>> another one as well as the highest set bit is no bigger than the one >>> specified by the given policydb data structure. It is doing it in >>> a bit-by-bit manner. So if the ebitmap structure has many bits set, >>> the iteration loop will be done many times. >>> >>> The current code can be rewritten to use a similar algorithm as the >>> ebitmap_contains() function with an additional check for the >>> highest set bit. The ebitmap_contains() function was extended to >>> cover an optional additional check for the highest set bit, and the >>> mls_level_isvalid() function was modified to call ebitmap_contains(). >>> >>> With that change, the perf trace showed that the used CPU time drop >>> down to just 0.08% (ebitmap_contains + mls_level_isvalid) of the >>> total which is about 100X less than before. >>> >>> 0.07% ls [kernel.kallsyms] [k] ebitmap_contains >>> 0.05% ls [kernel.kallsyms] [k] ebitmap_get_bit >>> 0.01% ls [kernel.kallsyms] [k] mls_level_isvalid >>> 0.01% ls [kernel.kallsyms] [k] find_next_bit >>> >>> The remaining ebitmap_get_bit() and find_next_bit() functions calls >>> are made by other kernel routines as the new mls_level_isvalid() >>> function will not call them anymore. >>> >>> This patch also improves the high_systime AIM7 benchmark result, >>> though the improvement is not as impressive as is suggested by the >>> reduction in CPU time spent in the ebitmap functions. The table below >>> shows the performance change on the 2-socket x86-64 system (with HT >>> on) mentioned above. >>> >>> +--------------+---------------+----------------+-----------------+ >>> | Workload | mean % change | mean % change | mean % change | >>> | | 10-100 users | 200-1000 users | 1100-2000 users | >>> +--------------+---------------+----------------+-----------------+ >>> | high_systime | +0.1% | +0.9% | +2.6% | >>> +--------------+---------------+----------------+-----------------+ >>> >>> Signed-off-by: Waiman Long <Waiman.Long@hp.com> >> >> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> >> > > Thank for the Ack. Will that patch go into v3.11?
I hope so, but that's up to Eric Paris, who maintains the kernel tree for SELinux changes these days.
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