linux-kernel - Re: [PATCH v7 2/2] clocksource: add J-Core timer/clocksource driver

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Date:   Tue, 4 Oct 2016 16:58:37 -0400
From:   Rich Felker <dalias@...c.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-sh@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v7 2/2] clocksource: add J-Core timer/clocksource driver

On Tue, Oct 04, 2016 at 12:06:23AM -0700, Paul E. McKenney wrote:
> On Mon, Oct 03, 2016 at 06:10:39PM -0400, Rich Felker wrote:
> > On Mon, Sep 26, 2016 at 11:27:14PM +0200, Daniel Lezcano wrote:
> > > On 26/09/2016 23:07, Rich Felker wrote:
> > > > Ping. Is there anything that still needs to be changed for this driver
> > > > to be acceptable?
> > > 
> > > It is on my radar. I'm reviewing it.
> > > 
> > > Can you elaborate the workaround mentioned in the changelog. I have been
> > > digging into the lkml@ thread but it is not clear if the issue is
> > > related to the time framework, the driver itself or whatever else. Can
> > > you clarify that ?
> > 
> > Do you have comments on any remaining issues other than this
> > workaround? If not I don't mind removing the workaround and trying to
> > solve the issue separately later. Let me know and either way I'll
> > submit a v8.
> 
> One question of interest to me is whether this patchset prevents the
> RCU CPU stall warnings that you are seeing.

With the 5ms minimum delta, I didn't observe any rcu_sched stall
warnings. At 2.5ms I thought it was gone but eventually saw one. With
the previous mindelta = 1, i.e. 1 hardware bus period, I get the
stalls regularly.

Rich