On 7/16/07, Roman Zippel <[email protected]> wrote:
On Mon, 16 Jul 2007, Jonathan Corbet wrote:
> > One possible problem here is that setting up that timer can be
> > considerably more expensive, for a relative timer you have to read the
> > current time, which can be quite expensive (e.g. your machine now uses the
> > PIT timer, because TSC was deemed unstable).
>
> That's a possibility, I admit I haven't benchmarked it. I will say that
> I don't think it will be enough to matter - msleep() is not a hot-path
> sort of function. Once the system is up and running it almost never
> gets called at all - at least, on my setup.
That's a bit my problem - we have to consider other setups as well.
Is it worth converting all msleep users behind their back or should we
just a provide a separate function for those who care?
As a driver author (2.4 timeframe, embedded platform, see gitinc.com
for the hardware description), I would rather msleep did what it says
it's going to do. If the current one can wait 20 times longer than you
ask for, then that's just broken.
> > One question here would be, is it really a problem to sleep a little more?
>
> "A little more" is a bit different than "twenty times as long as you
> asked for." That "little bit more" added up to a few seconds when
> programming a device which needs a brief delay after tweaking each of
> almost 200 registers.
Which driver is this? I'd like to look at this, in case there's some other
hidden problem.
"Hidden problem"? Lots of hardware has quiescent wait-time
requirements, to guarantee that whatever is going on it it's little
state machine head finally reaches a stable state. Waiting for those
changes to take effect before starting the next set of register
reprogramming is a common requirement -- on the hardware I've worked
with at least.
Ray
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