lkml.org 
[lkml]   [2002]   [Feb]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Lse-tech] NUMA scheduling
On Mon, 25 Feb 2002, Davide Libenzi wrote:

> On Mon, 25 Feb 2002, Larry McVoy wrote:
>
> > On Mon, Feb 25, 2002 at 10:55:03AM -0800, Martin J. Bligh wrote:
> > > > - The load_balancing() concept is different:
> > > > - there are no special time intervals for balancing across pool
> > > > boundaries, the need for this can occur very quickly and I
> > > > have the feeling that 2*250ms is a long time for keeping the
> > > > nodes unbalanced. This means: each time load_balance() is called
> > > > it _can_ balance across pool boundaries (but doesn't have to).
> > >
> > > Imagine for a moment that there's a short spike in workload on one node.
> > > By agressively balancing across nodes, won't you incur a high cost
> > > in terms of migrating all the cache data to the remote node (destroying
> > > the cache on both the remote and local node), when it would be cheaper
> > > to wait for a few more ms, and run on the local node?
> >
> > Great question! The answer is that you are absolutely right. SGI tried
> > a pile of things in this area, both on NUMA and on traditional SMPs (the
> > NUMA stuff was more page migration and the SMP stuff was more process
> > migration, but the problems are the same, you screw up the cache). They
> > never got the page migration to give them better performance while I was
> > there and I doubt they have today. And the process "migration" from CPU
> > to CPU didn't work either, people tended to lock processes to processors
> > for exactly the reason you alluded to.
> >
> > If you read the early hardware papers on SMP, they all claim "Symmetric
> > Multi Processor", i.e., you can run any process on any CPU. Skip forward
> > 3 years, now read the cache affinity papers from the same hardware people.
> > You have to step back and squint but what you'll see is that these papers
> > could be summarized on one sentence:
> >
> > "Oops, we lied, it's not really symmetric at all"
> >
> > You should treat each CPU as a mini system and think of a process reschedule
> > someplace else as a checkpoint/restart and assume that is heavy weight. In
> > fact, I'd love to see the scheduler code forcibly sleep the process for
> > 500 milliseconds each time it lands on a different CPU. Tune the system
> > to work well with that, then take out the sleep, and you'll have the right
> > answer.
>
> I made this test on 8 way NUMA machines ( thx to OSDLAB ). When a CPUs

s/NUMA/SMP/



- Davide


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

\
 
 \ /
  Last update: 2005-03-22 13:24    [W:0.068 / U:6.784 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site