Well... You'll also have to cover stuff like "sigreturn" etc, which _can_
be quite timing critical.
And there's also the issue of non-system-calls. Things like the return
from the page fault handler could very well be speeded up using SYSEXIT,
by just making SYSEXIT part of the regular return sequence. Basically,
change the "restore_all" code in arch/i386/kernel/entry.S to dynamically
switch between "iret" and "SYSEXIT" - then _every_ normal kernel exit gets
No special cases. You lose by having three comparisons: you need to check
DS, SS and weflags. But that's on the order of a few cycles, and you win
by using SYSEXIT whenever possible - including interrupts, page faults,
I agree that you could _additionally_ have the simple-fast-system-call
case, but I wonder if the few cycles you save by avoiding the comparison
is even worth it.
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