Date: Tue, 05 Feb 2002 20:52:11 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: John Polstra <jdp@polstra.com> Cc: hackers@freebsd.org Subject: Re: A question about timecounters Message-ID: <92661.1012938731@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 05 Feb 2002 11:44:15 PST." <200202051944.g15JiFw04286@vashon.polstra.com>
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In message <200202051944.g15JiFw04286@vashon.polstra.com>, John Polstra writes:
>OK, adding the splhigh() around the body of microuptime seems to have
>solved the problem. After 45 minutes of running the same test as
>before, I haven't gotten a single message. If I get one later, I'll
>let you know.
Ok, so we know where the bogotism happens, now to identify it...
>I don't follow that. As I read the code, the "current" timecounter
>is only advanced every second -- not every 1/HZ seconds. Why should
>more of them be needed when HZ is large?
No, only if you have set tco_method to one, if tco_method is zero (default)
we update the timecounter every HZ.
>> You didn't say if you ran with standard NTIMECOUNTER right now,
>> but 5 would be awfully short time at HZ=10000: 500 usec...
>
>Well, microseconds aren't what they used to be ... :-) But isn't it
>true that the current timecounter only advances every second? I think
>I have 5 seconds, not 5/HZ seconds.
Depends on your tco_method...
Could you try this combination:
NTIMECOUNTER = HZ (or even 5 * HZ)
tco_method = 0
no splhigh protection for microuptime() ?
The reason why tco_method=1 isn't nice is that we loose the ability to use
1/hz precision cached timestamps in the get*() funtions.
Btw, regarding the volatile thing:
If I do
extern volatile struct timecounter *timecounter;
microtime()
{
struct timecounter *tc;
tc = timecounter;
The compiler complains about loosing the volatile thing.
How do I tell it that it is the contents of the "timecounter" pointer which
is volatile, but now what it points at ? I don't want the "tc" pointer to
be volatile because it obviously isn't. Do I really need to cast it ?
tc = (struct timecounter *)timecounter;
That looks silly to me...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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