Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8

[Eugeny S. Mints]

Scott Wood wrote:
> On Thu, Oct 21, 2004 at 12:49:30PM -0400, john cooper wrote:
>
> > It would seem a mutex ownership list still needs to be maintained.
> > Doing so in unordered priority will give a small fixed insertion
> > time, but will require an exhaustive search in order to calculate
> > maximum priority. Doing so in priority order will require an
> > average of #mutex_owned / 2 for the insertion, and gives a fixed
> > time for maximum priority calculation. The latter appears to offer
> > a performance benefit to the degree the incoming priorities are
> > random.
>
>
> If you keep it in priority order, then you're paying the O(n) cost
> every time you acquire a lock.  If you keep it unordered and only
> search it when you need to recalculate a task's priority after a lock
> has been released (or priorities have been changed), you pay the cost
> much less often.  Plus, the number of locks held by any given thread
> should generally be very small.
As to locks held by any given thread - it's not always true - take a 
look at mm/filemap.c locks nesting map in comments.

                       Eugeny



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