Re: [PATCH 0/2] MIPS: Move signal return trampolines off the stack.

[David VomLehn <dvomlehn@cisco.com>]

On Tue, Apr 21, 2009 at 02:30:55PM -0700, David Daney wrote:
> This patch set (against 2.6.29.1) creates a vdso and moves the signal
> trampolines to it from their previous home on the stack.
>
> Tested with a 64-bit kernel on a Cavium Octeon cn3860 where I have the
> following results from lmbench2:
>
> Before:
> n64 - Signal handler overhead: 14.517 microseconds
> n32 - Signal handler overhead: 14.497 microseconds
> o32 - Signal handler overhead: 16.637 microseconds
>
> After:
>
> n64 - Signal handler overhead: 7.935 microseconds
> n32 - Signal handler overhead: 7.334 microseconds
> o32 - Signal handler overhead: 8.628 microseconds

Nice numbers, and something that will be even more critical as real-time
features are added and used!

> Comments encourged.

Only one comment, which I would not want to hold up acceptance:
based on some numbers sent out recently, it looks like the kernel is
experiencing some performance issues with exec() and I think this change will
make it slightly slower. You could avoid this by deferring installation of
the trampoline to the first use of a system call that registers a signal
handler.

David VomLehn