linux-kernel - Re: [PATCH v5] rcutorture: Perform more frequent testing of ->gpwrap

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Message-ID: <fcf1bc68-d8f1-4efc-9315-d333cf6ddcc1@nvidia.com>
Date: Mon, 21 Apr 2025 16:27:53 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: paulmck@...nel.org
Cc: linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
 Frederic Weisbecker <frederic@...nel.org>,
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
 Joel Fernandes <joel@...lfernandes.org>,
 Josh Triplett <josh@...htriplett.org>, Boqun Feng <boqun.feng@...il.com>,
 Uladzislau Rezki <urezki@...il.com>, Steven Rostedt <rostedt@...dmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 Davidlohr Bueso <dave@...olabs.net>, rcu@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v5] rcutorture: Perform more frequent testing of ->gpwrap



On 4/21/2025 2:32 PM, Paul E. McKenney wrote:
> On Mon, Apr 21, 2025 at 01:53:17PM -0400, Joel Fernandes wrote:
>> On 4/21/2025 1:47 PM, Joel Fernandes wrote:
>>> Currently, the ->gpwrap is not tested (at all per my testing) due to the
>>> requirement of a large delta between a CPU's rdp->gp_seq and its node's
>>> rnp->gpseq.
>>>
>>> This results in no testing of ->gpwrap being set. This patch by default
>>> adds 5 minutes of testing with ->gpwrap forced by lowering the delta
>>> between rdp->gp_seq and rnp->gp_seq to just 8 GPs. All of this is
>>> configurable, including the active time for the setting and a full
>>> testing cycle.
>>>
>>> By default, the first 25 minutes of a test will have the _default_
>>> behavior there is right now (ULONG_MAX / 4) delta. Then for 5 minutes,
>>> we switch to a smaller delta causing 1-2 wraps in 5 minutes. I believe
>>> this is reasonable since we at least add a little bit of testing for
>>> usecases where ->gpwrap is set.
>>>
>>> Tested-by: Paul E. McKenney <paulmck@...nel.org>
>>> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
>>> ---
>>> v4->v5
>>>  - Added gpwrap_lag torture param to turn off entire test.
>>>  - replaced references to 'ovf' with 'gpwrap lag'.
>>>
>>> Will move this to my rcu/torture-for-6.16 and update my rcu/for-next branches.
>>>  
>>>  .../admin-guide/kernel-parameters.txt         |  5 ++
>>>  kernel/rcu/rcu.h                              |  4 ++
>>>  kernel/rcu/rcutorture.c                       | 72 ++++++++++++++++++-
>>>  kernel/rcu/tree.c                             | 34 ++++++++-
>>>  kernel/rcu/tree.h                             |  1 +
>>>  5 files changed, 113 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index 76e538c77e31..e1d11b6595fd 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -5657,6 +5657,11 @@
>>>  			are zero, rcutorture acts as if is interpreted
>>>  			they are all non-zero.
>>>  
>>> +	rcutorture.gpwrap_lag= [KNL]
>>> +			Enable grace-period wrap lag testing. Setting
>>> +			to false prevents the gpwrap lag test from
>>> +			running.
>>> +
>> FYI, I added docs for the additional params here as well:
> 
> Even better, thank you!
> 
>> +       rcutorture.gpwrap_lag= [KNL]
>> +                       Enable grace-period wrap lag testing. Setting
>> +                       to false prevents the gpwrap lag test from
>> +                       running.
>> +
>> +       rcutorture.gpwrap_lag_gps= [KNL]
>> +                       Set the value for grace-period wrap lag during
>> +                       active lag testing periods. This controls how many
>> +                       grace periods differences we tolerate between
>> +                       rdp and rnp's gp_seq before setting overflow flag.
> 
> I suggest adding the default, as well as the default when no testing
> is taking place.
Will do, thanks.

 - Joel