Performance issue
Scott Long
scottl at samsco.org
Mon May 9 10:07:19 PDT 2005
Ewan Todd wrote:
>>>Whereas, the typical result for the new rig looked more like
>>>
>>> 105.36 real 71.10 user 33.41 sys
>>> ...
>>> 10548 involuntary context switches
>>>
>>>
>>
>>First of all, make sure that you have WITNESS and INVARIANTS off in your
>>kernel. You might also want to recompile your kernel with the SMP
>>option turned off.
>>
>>Scott
>
>
> First of all, thanks to Mike Tancsa for suggesting 5.4 RC4 and to Pete
> French for running the test independently on the higher spec machines
> with 5.4 RC4 on them, confirming the system time thing, ruling out an
> AMD problem, dissociating the system time result from the context
> switching, and saving me the trouble of rediscovering the same problem
> on 5.4 RC4.
>
> This is my first foray into the public world of FreeBSD discussion
> lists, and I am encouraged by the helpfulness of the response.
>
> Scott, the 5.3 kernel I had was a essentially a GENERIC release
> kernel, with about 100 options commented out. WITNESS and INVARIANTS
> are off by default, which I confirmed by looking through `sysctl -a`.
> However, I was curious to see what I would get if I switched them on,
> so I added these options and recompiled the kernel:
>
> options KDB
> options DDB
> options INVARIANTS
> options INVARIANT_SUPPORT
> options WITNESS
> options WITNESS_SKIPSPIN
>
> The result, below, has essentially the same user time (or just less,
> if that makes any sense), but tripled system time. The context
> switches are consistent with the one-per-10msec I saw before. Is
> there anything useful I can do while I still have the kernel debug
> options on?
>
> -e
>
>
> 172.29 real 67.53 user 103.07 sys
> 23376 maximum resident set size
> 659 average shared memory size
> 20805 average unshared data size
> 127 average unshared stack size
> 5402 page reclaims
> 0 page faults
> 0 swaps
> 0 block input operations
> 0 block output operations
> 0 messages sent
> 0 messages received
> 0 signals received
> 0 voluntary context switches
> 17234 involuntary context switches
>
>
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?
Scott
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