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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: Thu, 04 May 2017 16:07:14 -0500	[thread overview]
Message-ID: <1493932034.25397.37.camel@buserror.net> (raw)
In-Reply-To: <1493873917-7484-1-git-send-email-karim.eshapa@gmail.com>

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?

-Scott

  reply	other threads:[~2017-05-04 21:07 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 [this message]
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

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