Couldn't you mark the FPU as unused for the duration of the
handler, and let the lazy FPU mechanism save the state when it is used
by the signal handler?
> And yes, this signal handler thing is clearly visible on benchmarks.
> MUCH too clearly visible. I just didn't see any safe alternatives
> (and I still don't ;( )
I use SEGVs to trap access to read-only pages for garbage collection,
and I know I'm not the only one. That's a lot of SEGVs...
Fwiw, I have timed SIGSEGV handling time on Linux on various Intel CPUs,
on a PA-RISC running HP-UX and on a few Sparcs running Solaris. Linux
came out faster in all cases. Best case: 8 microseconds to trap a page
fault, handle the SEGV and mprotect() one page (600MHz P3). Worst case:
37 microseconds (133MHz Pentium).
That's about 5000 cycles. I'm sure we can do better than that.
For sophisticated user space uses, like the above, I'd like to see
a trap handling mechanism that saves only the _minimum_ state.
Userspace can take care of the rest. Maybe even without a sigreturn in
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