Memory Performance Issue with Fedora Core 2 Kernels

[James Wilkinson]

James Foris wrote:
> I have run into an issue with memory bandwidth using the Fedora Core
> 2 kernels and I need help.  I don't know what is wrong, but something
> killed performance of my custom driver when I ported it from RedHat 7.3
> to Fedora Core 2.  I believe I have narrowed it down to the kernel.
> 
> My driver requires a large amount of contiguous physical memory for
> DMA from a PCI device.  I use the 'mem=YYY' command line parameter to
> reserve the top of physical RAM for my driver.  Then I allow mapping
> via mmap() calls to user space.  The user space app then uses this
> pointer to save the data to disk.
<snip> 
> I have tried this on several platforms and kernels and the results vary,
> but the common denominator seems to be:
> 
>     Fedora kernel + 32-bit Intel = poor performance (see below)

So this *isn't* a problem with Linus' 2.6 kernels from kernel.org?

Wild guess: have you tried turning off the 4G+4G support in the kernel
(requires a recompile)?

HTH,

James.

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