[ivtv-users] Memory Usage

[Andy Walls]

On Thu, 2009-11-05 at 09:18 -0600, Steve Gunther wrote:
> I am modifying my ivtv settings to increase buffer size.  I am using
> the following string;
> 
> options ivtv enc_yuv_buffers=8 enc_mpg_buffers=48 enc_vbi_buffers=16
> enc_pcm_buffers=960
> 
> So by my math 8MB YUV + 48M MPG + 16M VBI + 960k = ~73M per tuner.
> 
> I have four tuners...
> 
> After boot I;
> 
> sudo rmmod ivtv
> 
> My memory usage is at 435672k used.  After I;
> 
> sudo modprobe ivtv
> 
> My memory usage is 1029156k used, for a difference of 593484k or ~148M
> per card.
> 
> 
> As far as the modino states the defaults should be So by my math 2MB
> YUV + 4M MPG + 1M VBI + 320k = ~7M per tuner.
> 
> With no modifier string my memory usage is 16M per card.
> 
> Any idea why my memory usage would be approximately double the
> assigned buffer size?

Likely because you don't have a hardware IOMMU, and thus the linux
kernel is using it's "software" IO MMU and allocating DMA bounce
buffers.

That's just a guess of course.

If you are upping the memory for buffers because you are worried that
you CPU can't keep up, be aware that I believe software bounce buffers
require the CPU to do memcpy()'s of the contents of the buffers to get
them to the ivtv driver.

Regards,
Andy

> -Steve