linux-kernel - RE:drivers:soc:fsl:qbman:qman.c: unsigned long jiffies value

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Message-Id: <1493514566-12920-1-git-send-email-karim.eshapa@gmail.com>
Date:   Sun, 30 Apr 2017 03:09:26 +0200
From:   Karim Eshapa <karim.eshapa@...il.com>
To:     oss@...error.net
Cc:     claudiu.manoil@....com, roy.pledge@....com,
        colin.king@...onical.com, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Karim Eshapa <karim.eshapa@...il.com>
Subject: RE:drivers:soc:fsl:qbman:qman.c: unsigned long jiffies value

On Sat, 29 Apr 2017 18:32:55 -0500, Scott Wood wrote:
>On Sat, 2017-04-29 at 22:43 +0200, Karim Eshapa wrote:
>
>> unsigned long jiffies value sorry for that.
>>
> You mean unsigned long msecs?
>

Yes, I mean usecs. 

>>
>> Signed-off-by: Karim Eshapa <karim.eshapa@...il.com>
>> ---
>>  drivers/soc/fsl/qbman/qman.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
>> index e0df4d1..6e1a44a 100644
>> --- a/drivers/soc/fsl/qbman/qman.c
>> +++ b/drivers/soc/fsl/qbman/qman.c
>> @@ -1084,7 +1084,7 @@ static int drain_mr_fqrni(struct qm_portal *p)
>>                * entries well before the ring has been fully consumed, so
>>                * we're being *really* paranoid here.
>>                */
>> -             unsigned int udel_time = jiffies_to_usecs(10000);
>> +             unsigned long udel_time = jiffies_to_usecs(10000);
>>  
>>               usleep_range(udel_time/2, udel_time);
>>               msg = qm_mr_current(p);

>If unsigned int isn't big enough, then unsigned long won't be either on 32-
>bit.  With such a long delay why not use msleep()?
>

I agree with you in long int.
After looking at Documentation/timers/timers-howto.txt I think
the msleep() is better as we actually have long delay.
may be we can use jiffies_to_msecs() with msleep() in case of we still have 
this large jiffies difference.

>As for the previous patch[1], you're halving the minimum timeout which may not
>be correct.
>
>

For the minimum timeout, I've read the following comments.

		 /*
                  * 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.
		  */
		  u64 now, then = jiffies;
		
		do {
	                now = jiffies;
                 } while ((then + 10000) > now);  

He needs to guarantee certain action so, he made a very large factor of saftey
therefore I've used sleep in range with approximate delay. But we still need 
the driver owner to define appropriate value to put.

>[1] When fixing a patch you've already posted that hasn't yet been applied,
>send a replacement (v2) patch rather than a separate fix.
>

Thanks so much, I'm just newbies :)


Karim