linux-kernel - RE: [Intel-wired-lan] [PATCH net-next v3 1/2] e1000e: factor out systim sanitization

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Message-ID: <c79639cd5a4c4907b83e2f5df50bd2bc@APLEX07.dom1.jhuapl.edu>
Date:	Wed, 27 Jul 2016 21:15:23 +0000
From:	"Woodford, Timothy W." <Timothy.Woodford@...apl.edu>
To:	"Avargil, Raanan" <raanan.avargil@...el.com>,
	Jarod Wilson <jarod@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Hall, Christopher S" <christopher.s.hall@...el.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
Subject: RE: [Intel-wired-lan] [PATCH net-next v3 1/2] e1000e: factor out
 systim	sanitization

>> This is prepatory work for an expanding list of adapter families that have occasional ~10 hour clock jumps when being used for PTP. Factor out the sanitization function and convert to using a feature (bug) flag, per suggestion from Jesse Brandeburg.
>> 
>> Littering functional code with device-specific checks is much messier than simply checking a flag, and having device-specific init set flags as needed.
>> There are probably a number of other cases in the e1000e code that could/should be converted similarly.
> 
> Looks ok to me.
> Adding Chris who asked what happens if we reach the max retry counter (E1000_MAX_82574_SYSTIM_REREAD)?
> This counter is set to 50. 
> Can you, for testing purposes, decreased this value (or even set it to 0) and see what happens?

I have one of the affected NICs.  I inserted some test code into the module to check the value of i after the for loop inside the sanitize function exits to check how many iterations of the loop were being run.  I ran a PTP test setup for a few hours with E1000_MAX_82574_SYSTIM_REREAD=50, and the maximum number was 5 iterations.
It looks like setting E1000_MAX_82574_SYSTIM_REREAD to 0 will just disable the return value checking and will have the same results as disabling the sanitization function.  I'll set the max retry counter to 1 and run an overnight test to see what happens.

Tim Woodford