Date: Mon, 09 May 2005 13:30:08 -0500 From: Jonathan Noack <noackjr@alumni.rice.edu> To: Pete French <petefrench@ticketswitch.com> Cc: freebsd-stable@freebsd.org Subject: Re: Performance issue Message-ID: <427FAC30.80507@alumni.rice.edu> In-Reply-To: <E1DVC6B-000FgV-9j@dilbert.firstcallgroup.co.uk> References: <E1DVC6B-000FgV-9j@dilbert.firstcallgroup.co.uk>
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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@alumni.rice.edu | OpenPGP: 0x991D8195
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