Re: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies.
From: Scott Wood
Date: Fri May 05 2017 - 02:33:46 EST
On Fri, 2017-05-05 at 08:01 +0200, Karim Eshapa wrote:
> > On 5/4/2017 5:07 PM, Scott Wood wrote:
> > > On Thu, 2017-05-04 at 06:58 +0200, Karim Eshapa wrote:
> > > > +ÂÂÂÂstop = jiffies + 10000;
> > > > +ÂÂÂÂ/*
> > > > +ÂÂÂÂÂ* if MR was full and h/w had other FQRNI entries to produce, we
> > > > +ÂÂÂÂÂ* need to allow it time to produce those entries once the
> > > > +ÂÂÂÂÂ* existing entries are consumed. A worst-case situation
> > > > +ÂÂÂÂÂ* (fully-loaded system) means h/w sequencers may have to do 3-4
> > > > +ÂÂÂÂÂ* other things before servicing the portal's MR pump, each of
> > > > +ÂÂÂÂÂ* which (if slow) may take ~50 qman cycles (which is ~200
> > > > +ÂÂÂÂÂ* processor cycles). So rounding up and then multiplying this
> > > > +ÂÂÂÂÂ* worst-case estimate by a factor of 10, just to be
> > > > +ÂÂÂÂÂ* ultra-paranoid, goes as high as 10,000 cycles. NB, we consume
> > > > +ÂÂÂÂÂ* one entry at a time, so h/w has an opportunity to produce new
> > > > +ÂÂÂÂÂ* entries well before the ring has been fully consumed, so
> > > > +ÂÂÂÂÂ* we're being *really* paranoid here.
> > > > +ÂÂÂÂÂ*/
> > >
> > > OK, upon reading this more closely it seems the intent was to delay for
> > > 10,000
> > > *processor cycles* and somehow that got turned into 10,000 jiffies
> > > (which is
> > > 40 seconds at the default Hz!).ÂÂWe could just replace this whole thing
> > > with
> > > msleep(1) and still be far more paranoid than was originally intended.
> > >
> > > Claudiu and Roy, any comments?
> > Yes the timing here is certainly off, the code changed a few times since
> > the comment was originally written.
> > An msleep(1) seems reasonable here to me.
> If the previous patch with msleep(1) is OK.
> can I send a patch to slightly change the comments.