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From: Roy Pledge <roy.pledge@nxp.com>
To: Scott Wood <oss@buserror.net>, Karim Eshapa <karim.eshapa@gmail.com>
Cc: Claudiu Manoil <claudiu.manoil@nxp.com>,
	"colin.king@canonical.com" <colin.king@canonical.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies.
Date: Thu, 4 May 2017 23:30:05 +0000	[thread overview]
Message-ID: <VI1PR04MB3216EC873ED7EB10F3D2CF9D86EA0@VI1PR04MB3216.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <1493932034.25397.37.camel@buserror.net>

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.

Roy
>
> -Scott
>
>

  reply	other threads:[~2017-05-04 23:30 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 [this message]
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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