Re: [PATCH v5] introduce macro spin_event_timeout()

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2009-03-10 at 19:22 -0500, Timur Tabi wrote:
> 
> Alan did have one valid point though.  Determining how long to loop
> for is architecture-specific.  Using jiffies is bad, because even one
> jiffy is too long.  Adding a udelay() inside the loop means that it
> only checks he condition every microsecond.  So the real solution is
> to use keep looping until a certain amount of time has passed.  This
> means using an architecture-specific timebase register.

> Now we can create a generic version of the function that uses jiffies,
> and then arch-specific versions where possible.  But Alan still needs
> to be convinced.  I already posted a length rebuttal to his email, but
> I haven't gotten a reply yet.
> 
There are several aspects here:

 - The amount of time to wait should be specified by the caller since
it's generally going to come from HW specs

 - The amount of time between the polls ... that could also be an
argument to the macro, not sure there

 - The precision of the actual wait calls... I vote for microseconds for
everything and udelay. The arch will do its best.

Cheers,
Ben.