Re: AllocateCommonBuffer slow on AMD Opteron

I may be barking up the wrong tree, but it could be that kernel-side
physical memory is too fragmented at the time you allocate the buffer.
I had a similar problem in my driver - I need huge dma areas for my 3D
volumes, but I don't use AllocateCommonBuffer - and sometimes things
would get pretty slow because the OS would take quite a while to
marshall the required contiguous memory.

What I do is, I allocate a large (tens of megabytes) slab of
contiguous physical memory at driver initialization time. I
suballocate my contiguous memory from that slab. The performance
problem is gone!

Alberto.



On Mar 13, 7:20 am, Olivier <o.anto...@xxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Hello,

I am developing drivers for a PCI Express device and - for performances
reasons - I have to allocate quite huge (~8MB) DMA buffers. I know, this is
not the recommended method but in my case I do not have any other choice.

While everything goes very well on Intel processors, I encounter systematic
system freezes for 2-5 seconds during execution of AllocateCommonBuffer on
AMD Opteron machine.

Any idea why?

Thanks,

Olivier

.

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