Re: Modular SysV IPC, testers wanted [patch]

Zack Weinberg (
Sat, 05 Dec 1998 15:40:37 -0500

>I read that the patch uses a layer to detect IPC usage request or
>something similar. In this case it will slow IPC calls, won't it ?

Yes, there is additional overhead when IPC is a module. If the module
is loaded, the overhead is one test and one function call. If the
module isn't loaded, request_module is invoked and the overhead is
astronomical, but that can't happen in your inner loop.

The overhead when the module is loaded could be reduced by not
creating another stack frame. I don't know if GCC has extensions for
that; if it doesn't, the hooks would need to be in assembler. I wrote
some lmbench tests, which indicate that the overhead when the module
is loaded is lost in the noise, so I'm inclined not to bother.


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