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Date: Wed, 25 Jul 2001 13:03:27 +0200
From: Damien TOURAINE <damien.touraine@limsi.fr>
Organization: LIMSI-CNRS
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To: landley@webofficenow.com
CC: "Richard B. Johnson" <root@chaos.analogic.com>,
        linux-kernel@vger.kernel.org
Subject: Re: Call to the scheduler...
In-Reply-To: <Pine.LNX.3.95.1010724134717.32263A-100000@chaos.analogic.com> <01072415121901.00631@localhost.localdomain>
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Rob Landley wrote:

>On Tuesday 24 July 2001 13:54, Richard B. Johnson wrote:
>
>>Try sched_yield(). Accounting may still be messed up so the process
>>may be 'charged' for CPU time that it gave up. Also, usleep(n) works
>>very well with accounting working.
>>
>>This works, does not seem to load the system, but `top` shows
>>99+ CPU time usage:
>>
>>main()
>>{
>>    for(;;) sched_yield();
>>
>>}
>>
>This may not be an accounting problem.  If the system has nothing else to do, 
>it'll just re-schedule your yielding thread.
>
>How much of that 99% cpu usage is user and how much of it is system?  
>Basically what the above does is beat the scheduler to death...
>
In my case, as the process/thread that call the "sched_yield();" 
function "actively" waits for another process/thread finish its job, the 
process won't be the only one in the queue of activ job ...
Then, it won't use 99% of the time ...

>>This works and `top` shows nothing being used:
>>
>>main()
>>{
>>
>>    for(;;) usleep(1);
>>
>>}
>>
>And here you DO block for a bit without getting called back immediately.
>
However, I would like to know the scheduler frequency to switch between 
tasks.
If it's above 1 us, the usleep don't match my requirements ...

However, thanks for your quick and pertinent answer !

Friendly
    Damien TOURAINE


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