Re: [PATCH v2] drivers:soc:fsl:qbman:qman.c: Sleep instead of stuck hacking jiffies.
From: Roy Pledge
Date: Thu May 04 2017 - 19:30:26 EST
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.