linux-kernel - Re: [patch 3/3] xtensa: ccount clocksource

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20090303195401.GA2654@cmpxchg.org>
Date:	Tue, 3 Mar 2009 20:54:01 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Daniel Walker <dwalker@...o99.com>
Cc:	Johannes Weiner <jw@...ix.com>, Chris Zankel <chris@...kel.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 3/3] xtensa: ccount clocksource

On Tue, Mar 03, 2009 at 09:55:45AM -0800, Daniel Walker wrote:
> On Tue, 2009-03-03 at 16:30 +0100, Johannes Weiner wrote:
> > @ -29,6 +30,19 @@ unsigned long ccount_per_jiffy;              /* per 
> >  unsigned long nsec_per_ccount;         /* nsec per ccount increment
> > */
> >  #endif
> >  
> > +static cycle_t ccount_read(void)
> > +{
> > +       return (cycle_t)get_ccount();
> > +}
> > +
> > +static struct clocksource ccount_clocksource = {
> > +       .name = "ccount",
> > +       .rating = 200,
> > +       .read = ccount_read,
> > +       .mask = CLOCKSOURCE_MASK(32),
> > +       .mult = NSEC_PER_CCOUNT,
> > +};
> 
> You don't want to use the shift field?

Thanks for pointing it out.

To make sure I understood this:

If shift is 0, then a walltime adjustment would be done in 1/2^0
steps, meaning an adjustment of counting one nanosecond more or less
per ccount.

To give this a finer granularity and smooth out adjustments, the shift
should be a trade-off between too much adjustment and no adjustment
progress in a sane amount of time (and, of course, to stay within
bounds of the used type).

Does that make sense?

I found a patch of yours that introduced clocksource_hz2shift() but it
seems it hasn't been merged (yet).  Is it yet to get integrated?

Thanks in advance,

	Hannes
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/