[Elphel-support] Is there a way to assign a higher priority to an application on the Elphel board?

[Harry Kim]

Hi Andrey,

For your information, I attached a simple program that writes data chunk of
200KB 10,000 times to a CF card connected to the Elphel board.

With this program, I have noticed maximum 3 second writing time.
And I had the similar result on my Linux machine.
I like to understand why it takes 3 seconds although it is rare.

Do you have any idea?

Thanks,
Harry

On Thu, Mar 12, 2015 at 6:09 PM, Harry Kim <hkim at redzone.com> wrote:

> I just want to see if writing speed to a CF card can significantly change
> when a highest priority is assigned to my application.
>
> According to the link, it seems like I can use "renice" instead of nice
> for my purpose.
>
> Thanks!
>
> On Thu, Mar 12, 2015 at 5:32 PM, support-list <
> support-list at support.elphel.com> wrote:
>
>> Hello Harry,
>>
>> Which process do you want to have low priority? What kind of problems do
>> you have with insufficent CPU power? As we already found the CF card
>> timeouts are internal to the card (I noticed similar ~3 sec timeouts with
>> the modern SD card we use in the new 10393 camera). The internal buffer is
>> set 19MB, so if you know the average compressed frame size (in bytes) and
>> the frame rate you may calculate how long the buffer can accumulate data
>> without loosing data - normally 19MB should be enough.
>>
>> There are not many processes that can use much of the CPU (much of the
>> activity is inside the kernel), and it depends on the applications you
>> really need.
>>
>> How do you use the images/video from the camera? Do you stream it out
>> over the network or record in the camera?
>> These two processes are handled by the two different applications, and
>> for recording I would suggest to use camogm, not the streamer. If you only
>> record, and not stream out simultaneously you may disable streamer
>> completely. That will still allow you to acquire images over the network
>> with minimal overhead.
>>
>> There is also an autoexposure daemon running - you may disable it if you
>> control the exposure/white balance manually
>>
>> PHP, web server do not eat up CPU when not specifically requested by the
>> host, and there is nothing like Firefox or Flash running in the camera :-)
>>
>> And yes, default busybox (used in the camera as in most other embedded
>> systems) configuration does not have nice command - you may read some
>> discussion here: https://communities.intel.com/message/265279
>>
>> All the above  considerations are for the currently used firmware, really
>> old legacy code (more than 6-7 years old) had different applications, FPGA
>> clock rate and running software.
>>
>> Andrey
>>
>>
>>
>
>
> --
> Best regards,
>
> Harry Kim
> Senior Embedded Software Engineer
> RedZone Robotics Inc.
> 91 43rd Street, Suite 250
> Pittsburgh, PA 15201
>
> office 412-927-3456 or 412-476-8980 x214   cell 412-897-0066
> hkim at redzone.com
> www.redzone.com
>
>
>


-- 
Best regards,

Harry Kim
Senior Embedded Software Engineer
RedZone Robotics Inc.
91 43rd Street, Suite 250
Pittsburgh, PA 15201

office 412-927-3456 or 412-476-8980 x214   cell 412-897-0066
hkim at redzone.com
www.redzone.com
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