Re: [PATCH 06/13] writeback: bdi write bandwidth estimation

[Peter Zijlstra]

On Wed, 2010-11-17 at 15:38 -0800, Andrew Morton wrote:
> On Thu, 18 Nov 2010 00:24:59 +0100
> Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> 
> > On Wed, 2010-11-17 at 15:08 -0800, Andrew Morton wrote:
> > > On Wed, 17 Nov 2010 12:27:26 +0800
> > > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > > 
> > > > +     w = min(elapsed / (HZ/100), 128UL);
> > > 
> > > I did try setting HZ=10 many years ago, and the kernel blew up.
> > > 
> > > I do recall hearing of people who set HZ very low, perhaps because
> > > their huge machines were seeing performance prolems when the timer tick
> > > went off.  Probably there's no need to do that any more.
> > > 
> > > But still, we shouldn't hard-wire the (HZ >= 100) assumption if we
> > > don't absolutely need to, and I don't think it is absolutely needed
> > > here.  
> > 
> > People who do cpu bring-up on very slow FPGAs also lower HZ as far as
> > possible.
> 
> 	grep -r "[^a-zA-Z0-9_]HZ[ ]*/[ ]*100[^0-9]" .

Maybe they've got a patch-kit somewhere,. I'll ask around. It would be
nice to have that sorted.


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