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From: Karim Eshapa <karim.eshapa@gmail.com>
To: oss@buserror.net
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,
	Karim Eshapa <karim.eshapa@gmail.com>
Subject: RE: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies.
Date: Fri,  5 May 2017 08:01:54 +0200	[thread overview]
Message-ID: <1493964114-11296-1-git-send-email-karim.eshapa@gmail.com> (raw)
In-Reply-To: <1493873917-7484-1-git-send-email-karim.eshapa@gmail.com>

>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.

Thanks,
Karim

  parent reply	other threads:[~2017-05-05  6:02 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       ` Karim Eshapa [this message]
2017-05-05  6:33         ` [PATCH v2] " Scott Wood

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