Date: Fri, 28 Oct 2005 13:24:30 -0400 From: Chuck Swiger <cswiger@mac.com> To: Robert Watson <rwatson@FreeBSD.org> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, David Xu <davidxu@freebsd.org>, current@freebsd.org Subject: Re: Timers and timing, was: MySQL Performance 6.0rc1 Message-ID: <43625ECE.7010804@mac.com> In-Reply-To: <20051028144307.X53858@fledge.watson.org> References: <32412.1130505646@critter.freebsd.dk> <436229CF.6040001@freebsd.org> <20051028144307.X53858@fledge.watson.org>
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Robert Watson wrote:
> On Fri, 28 Oct 2005, David Xu wrote:
>> Poul-Henning Kamp wrote:
>>>> On the other hand, a lower risk change might be to simply add a new
>>>> CLOCK_ type for lower resolution, and have a timer synchronize a
>>>> variable to the system clock once every 1/10 of a second. This
>>>> avoids having to muck with VM layout, etc.
>>>
>>> Is the CLOCK_* namespace ours to muck about with in the first place?
>>>
>> I prefer this way, can you implement it? The global page idea is a
>> complex, someone can slowly work on it, there are many things can be
>> done, for example, fast syscall using sysenter/sysexit.
>
> I'm happy to take a stab at this.
>
> We still need someone to grab the context switch time keeping by the
> horns and Do Something, though.
If I understand what was said earlier, the getmicrotime() kernel function ought
to maintain the time at "(~ 1 msec)" precision. Could getmicrotime() be
exported as a syscall, so that we could do something like this:
--- lib/libc/gen/time.c~ Fri Jul 18 22:53:46 2003
+++ lib/libc/gen/time.c Fri Oct 28 13:04:26 2005
@@ -47,7 +47,8 @@
struct timeval tt;
time_t retval;
- if (gettimeofday(&tt, (struct timezone *)0) < 0)
+ getmicrotime(&tt);
+ if (tt.tv_sec == 0)
retval = -1;
else
retval = tt.tv_sec;
Note that this might even cause time(2) to return an error if the system is
using dummyclock, which could be considered a feature. :-)
--
-Chuck
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