Re: Real-time problem due to IO congestion.

[Takashi Ikebe <ikebe.takashi@lab.ntt.co.jp>]

I see.
The program which I tested is just sample, and I wanted to know the 
phenomena is spec or bug.
I also understand that this problem is spec, and need to apply some 
buffering to such applications.

Thank you.

Andrew Morton wrote:
> Takashi Ikebe <ikebe.takashi@lab.ntt.co.jp> wrote:
> 
>>There are 2 type processes in test environment.
>> 1. The real-time needed process (run on with high static priority)
>>     The process wake up every 10ms, and wake up, write some log (the
>> test case is current CPU clock via tsc) to the file.
>>
>> 2. The process which make IO load
>>     The process have large memory size, and kill the process with dumping.
>>     The process's memory area exceeds 70% of whole physical
>> RAM.(Actually 1.5GB memory area while whole RAM is 2GB)
>>
>> Whenever during dumping, the real-time needed process sometimes stop for
>> long time during write system call. (sometimes exceeds 1000ms)
> 
> 
> The writeback code does attempt to give some preference to realtime tasks
> (in get_dirty_limits()), but it can only work up to a point.
> 
> Frankly, your application is poorly designed.  If you want sub-10ms
> responsiveness you shouldn't be doing disk I/O.  The realtime task should
> hand the data off to a non-realtime task for writeout, with suitable
> amounts of buffering in between.

-- 
Takashi Ikebe