On Thu, Nov 08, 2007 at 10:11:21AM +0100, Peter Zijlstra wrote:
> On Wed, 2007-11-07 at 18:20 -0600, Matt Mackall wrote:
>
> > This and other cases
> > (lots of per_cpu users, IIRC) actually want a migrate_disable() which
> > is a proper subset.
>
> The disadvantage of migrate_disable() is that it complicates the
> load-balancer
Hmm, I'm surprised it's more than a one-liner. Something like
if (cannot_migrate(task))
continue;
But I'm certainly not the expert here. Perhaps this one-liner introduces the
"unplannable O(N) overhead" Ingo mentions in the email you referenced.
> but more importantly, that it does bring a form of latencies with it
> that are hard to measure. Using preempt_disable() for these current
> per-cpu users basically forces them to keep it short.
Ok, so maybe we've got implementation issues to tackle. But still: a)
preempt_disable is inherently misdocumentation (preemption is not the
real problem) and b) preemption is a bigger hammer than needed. At the
very least, we should introduce migrate_disable as an alias for
preempt_disable so we can document intent.
At any rate, in the current context, we're talking about actually
disabling preempt in a *delay loop*. Let's find a fix for that.
> Also see:
> http://lkml.org/lkml/2007/7/23/338
Heh, I'd completely forgotten about this thread and thought I was
having an original idea! Must have never seen Ingo's followup.
Ingo's complaint about it being "a per-task BKL" is interesting. I've
occassionally wondered if it makes sense to make some of these
primitives take a "documentation parameter" - a pointer to an object
that does nothing more than indicate the object of interest.
--
Mathematics is the supreme nostalgia of our time.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
