Messages in this thread | | | Date | Tue, 26 Jun 2007 00:20:27 +0200 | From | "Jesper Juhl" <> | Subject | Re: [patch, v2.6.22-rc6] sys_time() speedup |
| |
On 26/06/07, Roman Zippel <zippel@linux-m68k.org> wrote: > Hi, > > On Mon, 25 Jun 2007, Jesper Juhl wrote: > > > > On Monday 25 June 2007, Ingo Molnar wrote: > > > > > > > the patch improves the sysbench OLTP macrobenchmark significantly: > > > > > > Has that any real practical relevance? > > > > > It seems to me that Ingo's patch offers slightly improved performance > > for any program using the time() system call, with no real drawbacks, > > so why wouldn't we want to use it? > > How do you come to the conclusion it has no real drawbacks?
His change to do_gettimeofday() will of course slow that path down a tiny bit since he's adding an extra 'if', but since it's wrapped in unlikely() and should hit at most one time pr second I would guess the performance impact of that to be negligible. The change to sys_time() does away with some local variables and replaces the call to do_gettimeofday() with a memory barrier and a simple read of xtime.tv_se. I find it hard to believe (although I have not tested it) that that wouldn't be faster than the original.
So that's how I came to that conclusion; just reading the patch, going over what it does in my head and thinking about it a bit. Not the most scientific of things I admit.
Even if it is not faster, what would make it slower? Have you spotted something I have not?
> Ingo provided no information about his test setup and his patch was a > little strange, so I can't say that yet. > What did you find strange about it? I'm currious. Sure it needs testing and of course it would be nice with some more details on Ingo's test setup.
-- Jesper Juhl <jesper.juhl@gmail.com> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |