Re: Why is mmap()ed reserved memory so slow?

[David Chau <dchau@mazunetworks.com>]

Dan Malek wrote:

> How about a little more info, like what kernel are you using and what are
> the parameters you are sending to mmap()?

Linux (none) 2.4.31 #412 SMP Fri Jul 15 16:26:05 EDT 2005 mips unknown
(unmodified kernel from linux-mips.org).
It's running on the SB1 on a Broadcom 1250 board.

I mmap() with:
int mem_fd = open("/dev/mem", O_RDWR);
void* mem_base =
    mmap(NULL, DRIVER_MEM_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
         mem_fd, DRIVER_MEM_PHYS_BASE);
Where driver_mem_phys_base = 253M, and driver_mem_size=1M.

> The better way to approach this is to place an mmap() function in the
> associated driver that works in conjunction with the application to gain
> shared access as you expect.  This also closes a hole where an errant
> application could write into unexpected places through /dev/mem.


Could you point me to an example of this so I can figure out how to do it?

Thanks,
David