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

[Waiman Long]

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@xxxxxx>
>
> Acked-by:  Stephen Smalley <sds@xxxxxxxxxxxxx>

Thank for the Ack. Will that patch go into v3.11?

Regards,
Longman
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