Re: [PATCH]O18.1int

Nick Piggin
2003-08-28T13:58:42Z

Guillaume Chazarain wrote:

>28/08/03 14:34:15, Nick Piggin <piggin@cyberone.com.au> wrote:
>
>>Guillaume Chazarain wrote:
>>
>>
>>>Hi Con (and linux-kernel),
>>>
>>>I noticed a regression wrt 2.6.0-test4 and 2.4.22 with this
>>>big context-switcher:
>>>
>>>
>>Hi Guillaume,
>>If you get the time, would you be able to try my patch? Thanks.
>>
>
>Here are the results for Nick's v8:
>
>top(1):
>
> 639 g 30 0 1336 260 1308 R 51.2 0.1 0:03.80 a.out
> 638 g 22 0 1336 260 1308 S 47.3 0.1 0:03.39 a.out
>
>User time (seconds): 0.57
>System time (seconds): 2.72
>Elapsed (wall clock) time (h:mm:ss or m:ss): 0:06.85
>Minor (reclaiming a frame) page faults: 17
>
>

Thanks Guillaume, so not very good. Its interesting that there can
be such a big difference in performance, but its a very simple app
so makes a good test for the specific regression.

In both Con's and my patches, the reader gets a bit more CPU. This
might be due to it preempting the writer more often on wakeups,
which would lead to more scheduling per work done and a regression.

If this is the case, I'm not sure the behaviour is too undesirable
though: its often very important for woken processes to be run
quickly. Its not clear that this workload is something we would
want to optimize for. Assuming the problem is what I guess.

I will take a look into it further when I get time tomorrow.