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From: Scott Wood <oss@buserror.net>
To: Karim Eshapa <karim.eshapa@gmail.com>
Cc: claudiu.manoil@nxp.com, roy.pledge@nxp.com,
	colin.king@canonical.com, linuxppc-dev@lists.ozlabs.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies.
Date: Fri, 05 May 2017 01:33:29 -0500	[thread overview]
Message-ID: <1493966009.25397.39.camel@buserror.net> (raw)
In-Reply-To: <1493964114-11296-1-git-send-email-karim.eshapa@gmail.com>

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:
> > > > +    stop = jiffies + 10000;
> > > > +    /*
> > > > +     * if MR was full and h/w had other FQRNI entries to produce, we
> > > > +     * need to allow it time to produce those entries once the
> > > > +     * existing entries are consumed. A worst-case situation
> > > > +     * (fully-loaded system) means h/w sequencers may have to do 3-4
> > > > +     * other things before servicing the portal's MR pump, each of
> > > > +     * which (if slow) may take ~50 qman cycles (which is ~200
> > > > +     * processor cycles). So rounding up and then multiplying this
> > > > +     * worst-case estimate by a factor of 10, just to be
> > > > +     * ultra-paranoid, goes as high as 10,000 cycles. NB, we consume
> > > > +     * one entry at a time, so h/w has an opportunity to produce new
> > > > +     * entries well before the ring has been fully consumed, so
> > > > +     * we're being *really* paranoid here.
> > > > +     */
> > > 
> > > 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!).  We 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.

Yes.

-Scott

      reply	other threads:[~2017-05-05  6:33 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-29 19:46 [PATCH] " Karim Eshapa
2017-04-29 20:43 ` [PATCH] drivers:soc:fsl:qbman:qman.c: unsigned long jiffies value Karim Eshapa
2017-04-29 23:32   ` Scott Wood
2017-04-30  1:09     ` Karim Eshapa
2017-05-04  4:58     ` [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies Karim Eshapa
2017-05-04 21:07       ` Scott Wood
2017-05-04 23:30         ` Roy Pledge
2017-05-05  5:45       ` [PATCH v3] " Karim Eshapa
2017-06-25  2:46         ` [v3] " Scott Wood
2017-06-27 16:38           ` Leo Li
2017-05-05  6:01       ` [PATCH v2] " Karim Eshapa
2017-05-05  6:33         ` Scott Wood [this message]

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