Memory Performance Issue with Fedora Core 2 Kernels

[John Dangler]

-----Original Message-----
From: fedora-list-bounces at redhat.com [mailto:fedora-list-bounces at redhat.com]
On Behalf Of James Foris
Sent: Monday, July 26, 2004 3:22 PM
To: fedora-list at redhat.com
Subject: Memory Performance Issue with Fedora Core 2 Kernels
...[snip]...

>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.

>Normally the user space app writes to disk using the mmap()'d pointer as
>the source.  With the new kernels these writes are taking way too long
>(around 20 MB/s).  Even when the write goes to /dev/shm, the speed is
>limited to around 20 MB/s.  A memcpy from the mmap()'d memory seems to
>have no such slowdown.

The bottleneck seems to be in i/o...

check the hdparm settings on the drive.

(memcpy will definitely run faster than disc i/o)

...[snip]...

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