Re: [PATCH] linux-2.5.43_vsyscall_A0

Jeff Dike
2002-10-20T00:52:51Z

andrea@suse.de said:
> What I suggested is an arch specific syscall to shutdown vsyscalls
> enterely for the current task and its childs,

Then I misunderstood.

> the vsyscall will call
> into the real syscall with sysenter, and you will be able to
> revirtualize gettimeofday/time like you do on x86 with ptrace.

And the task-specific fixmap entry would point to a page that makes the normal
system call?

> what do you mean that uml needs the vsyscalls more than the other
> archs?

Because its system calls are much slower than the host's. It would benefit
more from vsyscalls.

> I much prefer you to keep trapping the gettimeofday and time with
> ptrace after shutting down the vsyscalls for the current task, it's so
> much cleaner.

And so much slower.

> The overhead of ptrace cannot be your point, if that
> overhead is a showstopper uml isn't an option in the first place.

I don't plan on using ptrace forever. That overhead is going to shrink, and
vsyscalls are one way to make it shrink.

I intend to make UML perform by grabbing whatever improvements from wherever
I can get them, and if I can't get vsyscalls because they're not virtualizable,
then, from my point of view, their design is broken.

Jeff