Re: The disappearing sys_call_table export.

Christoph Hellwig
2003-05-05T10:13:03Z

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?