linux-kernel - Re: [PATCH 8/8] LinuxPPS: pps_gen_parport: Add check for bad clocksource.

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Message-ID: <20170304121945.06e7bbfd@brick.gerasiov.net>
Date:   Sat, 4 Mar 2017 12:19:45 +0300
From:   Alexander Gerasiov <gq@...msu.su>
To:     Rodolfo Giometti <giometti@...eenne.com>
Cc:     Andrey Drobyshev <immortalguardian1@...il.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 8/8] LinuxPPS: pps_gen_parport: Add check for bad
 clocksource.

Hello Rodolfo,

I should say, that I found this solution is not the best. For example on
high speed PCs (I think over 3GHz) 5 iteration is not enough and module
stops working after several hours. That makes it not user-friendly,
cause user had to calibrate and set failure_iterations manually.

It would be better to use pre-measured loops_per_jiffy (from delay.h)
some way.

On Sat, 4 Mar 2017 08:44:03 +0100
Rodolfo Giometti <giometti@...eenne.com> wrote:

> On 02/15/17 15:31, Andrey Drobyshev wrote:
> > From: Nikita Edward Baruzdin <nebaruzdin@...il.com>
> >
> > This commit is supposed to resolve the issue with hard lockups on
> > systems using jiffies as their clock source. Namely, it sets limits
> > on number of iterations clock source may remain unchanged (i. e.
> > not being updated for one reason or another, as it is with jiffies
> > clock source), and on unsuccessful getnstimeofday() polls as well.
> > In case limit is reached, we consider clock source incompatible
> > with this driver or unstable.
> >
> > Considering this issue to be fixed, un-BROKEN pps_gen_parport.
> >
> > For explanation of the problem see this thread on lkml:
> > https://lkml.org/lkml/2011/2/18/310
> >
> > Signed-off-by: Nikita Edward Baruzdin <nebaruzdin@....cs.msu.su>
> > Signed-off-by: Alexander GQ Gerasiov <gq@...msu.su>  
> 
> Acked-by: Rodolfo Giometti <giometti@...eenne.com>



-- 
Best regards,
 Alexander Gerasiov

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