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SubjectRe: [PATCH 1/2 v5] SELinux: Reduce overhead of mls_level_isvalid() function call
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?

Regards,
Longman


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