On Tue, 26 Jun 2007 19:08:27 +0200 (CEST) Roman Zippel <[email protected]> wrote:
> > This current ... interesting piece of Roman about a _single_ trivial
> > unlikely() branch in do_gettimeofday() borders on the ridiculous. My
> > patch might be wrong for various reasons, but that single
> > 'if (unlikely())' statement is not one of those reasons =B-)
>
> That's even more nonsense, that wasn't what my mail was about and Andrew
> understood me correctly, so you could have too.
umm, yeah. Ingo went a bit over the top there, IMO.
It boils down to: is sys_time() called at more or less than 1/2000th the
frequency of gettimeofday(), across the expected lifetime of 2.6.23 and
later? Ingo has a couple of (surprising) examples where the sys_time()
call frequency _is_ high, but whether that will remain true across 2.6.23
and later is an open question.
How does mysql call sys_time() at all, if time(2) uses the vsyscall page??
Will contemporary-to-2.6.23-and-later mysqls do this?
All this isn't super-trivial silliness, either. gettimeofday() is, for
many workloads, the kernel's most time-critical codepath bar none, I
believe.
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