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Date: Tue, 5 Mar 2002 20:34:43 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
X-X-Sender: davide@blue1.dev.mcafeelabs.com
To: Ben Greear <greearb@candelatech.com>
cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: a faster way to gettimeofday?
In-Reply-To: <Pine.LNX.4.44.0203052024540.1475-100000@blue1.dev.mcafeelabs.com>
Message-ID: <Pine.LNX.4.44.0203052033570.1475-100000@blue1.dev.mcafeelabs.com>
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On Tue, 5 Mar 2002, Davide Libenzi wrote:

> On Tue, 5 Mar 2002, Ben Greear wrote:
>
> >
> >
> > Davide Libenzi wrote:
> >
> > > On Tue, 5 Mar 2002, Ben Greear wrote:
> > >
> > >
> > >>I have a program that I very often need to calculate the current
> > >>time, with milisecond accuracy.  I've been using gettimeofday(),
> > >>but gprof shows it's taking a significant (10% or so) amount of
> > >>time.  Is there a faster (and perhaps less portable?) way to get
> > >>the time information on x86?  My program runs as root, so should
> > >>have any permissions it needs to use some backdoor hack if that
> > >>helps!
> > >>
> > >
> > > If you're on x86 you can use collect rdtsc samples and convert them to ms.
> > > You'll get even more then ms accuracy.
> >
> >
> > Can I do this from user space?  If so, any examples or docs
> > you can point me to?
> >
> > Also, I'm looking primarily for a speed increase, not an accuracy
> > increase.
>
>
>     #include <linux/timex.h>
>
>
>     unsigned long long mscurr;
>     cycles_t cys, cye, mscycles;
>     struct timespec ts1, ts2;
>
>     clock_gettime(CLOCK_REALTIME, &ts1);
>     cys = get_cycles();
>     sleep(1);
>     clock_gettime(CLOCK_REALTIME, &ts2);
>     cye = get_cycles();
>     mscycles = (cye - cys) / ((ts2.tv_sec - ts1.tv_sec) * 1000 +
> 		(ts2.tv_nsec - ts1.tv_nsec) / 1000000);
>
>
>
>     mscurr = ts2.tv_sec * 1000 + ts2.tv_nsec * 1000000 + (get_cycles() - cye) / mscycles;

it's obviously  ... ts2.tv_nsec / 1000000 ...



- Davide


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