Messages in this thread | | | Date | Mon, 5 May 2003 11:25:31 +0100 | From | Christoph Hellwig <> | Subject | Re: The disappearing sys_call_table export. |
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On Mon, May 05, 2003 at 11:33:36AM +0200, Terje Eggestad wrote: > 1. performance is everything.
then Linux is the wrong OS for you :)
> 2. We're making a MPI library, and as such we don't have any control > with the application.
I can't remember that the MPI spec tells anything about intercepting syscalls..
> 3b. the performance loss from copying from a receive area to the > userspace buffer is unacceptable. > 3c. It's therefore necessary for HW to access user pages. > 4. In order to to 3, the user pages must be pinned down. > 5. the way MPI is written, it's not using a special malloc() to allocate > the send receive buffers. It can't since it would break language binding > to fortran. Thus ANY writeable user page may be used.
so use get_user_pages.
> 6. point 4: pinning is VERY expensive (point 1), so I can't pin the > buffers every time they're used.
Umm, pinning memory all the time means you get a bunch of nice DoS attachs due to the huge amount of memory.
> 7. The only way to cache buffers (to see if they're used before and > hence pinned) is the user space virtual address. A syscall, thus ioctl > to a device file is prohibitive expensive under point 1.
That's a horribly b0rked approach..
Again, where's your driver source so we can help you to find a better approach out of that mess?
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