On Thu, Oct 17, 2002 at 04:04:37PM +0530, Nagaraj wrote:
> > If you don't do a blocking call, you will never leave CPU and thus the
> > machine will not do anything else. Even kernel threads won't run - they
> > are high priority normal proceses, not realtime.
>
> No, what i mean is do not block in the kernel, do a sleep()
> in the application.
>
> for( buff_index = i = 0; i < xfer_count; i++, buff_index =
> (buff_index+1)%MAX_BUFFERS ) {
>
> sleep(1000);
>
> read( buff_fd, (mbuff +buff_index*BUFF_SIZE), BUFF_SIZE );
>
> }
>
>
> The above code, ( u can see the details for my previous mails )
> sleeps till driver wakes it up through kill_fasync() which is there is an
> interrupt handler.
> Usually u get an interrupt after the devices xfers the data through DMA.
>
> So CPU time is given to other processes during that sleep.
>
> The sequence would be :
> driver uses ioctls to start xfer ( which is non blocking )
> Application sleeps during that time giving cpu to other processes.
> dma does the actual xfer and inform driver through interrupt.
> irq_handler informs application through fasync and sleep function
> immediately returns even before timeout ( refer man page for sleep ).
> So the switching time is minimal and also this guarantees contineous
> streaming
> of the video.
> This i hv tested for a bandwidth of 20 Mbits/sec.
That seems the interface is sane. However. Don't do sleep (btw: sleep
has second granularity - you would want usleep), do poll. It has
timeout, it wakes up on a signal, but in addition it allows you to wake
up whenever the network is ready to accept more data.
> I did that first with a blocking call, which resulted in frames being
> displayed with a delay ( due to the time between ur blocking call returning,
> and application refilling the buffer ).
-------------------------------------------------------------------------------
Jan 'Bulb' Hudec <bulb@ucw.cz>
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