On 04/10/2014 11:44 AM, Clark Williams wrote:
On Wed, 9 Apr 2014 15:19:22 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
This patch is built on top of the two other patches that I posted
earlier, which should not be as controversial.
If you have any benchmark on large machines I would be very happy if
you could test this patch against the unpatched version of -rt.
Cheers,
-- Steve
Steven
I wrote a program named whack_mmap_sem which creates a large (4GB)
buffer, then creates 2 x ncpus threads that are affined across all the
available cpus. These threads then randomly write into the buffer,
which should cause page faults galore.
I then built the following kernel configs:
vanilla-3.13.15 - no RT patches applied
rt-3.12.15 - PREEMPT_RT patchset
rt-3.12.15-fixes - PREEMPT_RT + rwsem fixes
rt-3.12.15-multi - PREEMPT_RT + rwsem fixes + rwsem-multi patch
My test h/w was a Dell R520 with a 6-core Intel(R) Xeon(R) CPU E5-2430
0 @ 2.20GHz (hyperthreaded). So whack_mmap_sem created 24 threads
which all partied in the 4GB address range.
I ran whack_mmap_sem with the argument -w 100000 which means each
thread does 100k writes to random locations inside the buffer and then
did five runs per each kernel. At the end of the run whack_mmap_sem
prints out the time of the run in microseconds.
The means of each group of five test runs are:
vanilla.log: 1210117
rt.log: 17210953 (14.2 x slower than vanilla)
rt-fixes.log: 10062027 (8.3 x slower than vanilla)
rt-multi.log: 3179582 (2.x x slower than vanilla)
Hi
I ran Clark's test on a machine with 32 CPUs: 2 Sockets, 8 core/socket + HT
On this machine I ran 5 different kernels:
Vanilla: 3.12.15 - Vanilla
RT: 3.12.15 + Preempt-RT 3.12.15-rt25
FIX: RT + rwsem fixes from rostedt
Multi: FIX + Multi-reader PI
Multi -FULL: Multi + CONFIG_PREEMPT=y
I ran the test with the same parameters that Clark used, 100 iterations
for each kernel. For each kernel I measure the min and max execution
time, along with the avg execution time and the standard deviation.
The result was:
+-------+---------+----------+----------+-----------+-------------+
| | Vanilla | RT | FIX | Multi | Multi -FULL |
--------+---------+----------+----------+-----------+-------------+
|MIN: | 3806754 | 6092939 | 6324665 | 2633614 | 3867240 |
|AVG: | 3875201 | 8162832 | 8007934 | 2736253 | 3961607 |
|MAX: | 4062205 | 10951416 | 10574212 | 2972458 | 4139297 |
|STDEV: | 47645 | 927839 | 943482 | 52579 | 943482 |
+-------+---------+----------+----------+-----------+-------------+
A comparative of avg case to vanilla:
RT - 2.10x (slower)
FIX - 2.06x (slower)
Multi - 0.70x (faster?)
Multi no PREEMPT_FULL - 1.02x (equals?)
As we can see, the patch gave good results on Preempt-RT, but my results
was a little bit weird, because the PREEMPT-RT + Multi patch became
faster than vanilla.
In the standard deviation, the patch showed a good result as well, with
the patch the std dev became ~17x smaller than on RT kernel without the
patch, which means less jitter.
-- Daniel
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