Performance issue

[Jonathan Noack]

On 5/9/2005 12:31 PM, Pete French wrote:
>>5.3 ships with SMP turned on, which makes lock operations rather 
>>expensive on single-processor machines.  4.x does not have SMP
>>turned on by default.  Would you be able to re-run your test with
>>SMP turned off?
> 
> 
> I just ran a test here with SMP turned of on 5.4-RC4 (GENERIC) I got the
> following result:
> 
>        67.52 real        41.13 user        26.16 sys
>       7034  involuntary context switches
> 
> i.e. it still has system time a a huge proportion of the total compared
> to the 4.11 kernel. Interesingly, after reading Holger Kipp's results
> I tried it on a genuine multi-processor box with SMP enabled running 5.3.
> He got a very small percentage of the time in sys (3.51 out of 81.90) but
> I got:
>       255.30 real       160.20 user        88.50 sys
> 
> Once again a far higher proprtion of the time spent in sys than you would
> expect.

I ran into a similar issue when attempting to thread a card game solver 
program I wrote.  Performance in early versions was horrific and I 
noticed tons of context switches.  I resolved the issue by allocating 
pools of memory beforehand.  This seems to point the finger to malloc 
and context switch overhead.

In any case, I believe this is related to threading.  Check your results 
with libthr instead.  The following are on my 2.53 GHz P4 which is 
running CURRENT from last night (with INVARIANTS on).

libpthread:
$ /usr/bin/time -al ./heapsort.py 1000000
0.9999928555
       124.04 real        65.71 user        48.47 sys
      23464  maximum resident set size
        680  average shared memory size
      21104  average unshared data size
        129  average unshared stack size
       5400  page reclaims
          0  page faults
          0  swaps
         15  block input operations
          0  block output operations
          4  messages sent
          0  messages received
          0  signals received
         21  voluntary context switches
      40274  involuntary context switches

libthr:
$ /usr/bin/time -al ./heapsort.py 1000000
0.9999928555
        79.75 real        50.63 user        25.34 sys
      23348  maximum resident set size
        679  average shared memory size
      21041  average unshared data size
        129  average unshared stack size
       5394  page reclaims
          1  page faults
          0  swaps
          2  block input operations
          0  block output operations
          3  messages sent
          0  messages received
          0  signals received
          7  voluntary context switches
      26113  involuntary context switches

-- 
Jonathan Noack | noackjr at alumni.rice.edu | OpenPGP: 0x991D8195
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