linux-kernel - Re: [PATCH v2 6/8] rcuscale: Add test for using call_rcu_lazy() to emulate kfree

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Date:   Tue, 12 Jul 2022 17:15:23 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     paulmck@...nel.org
Cc:     rcu <rcu@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Rushikesh S Kadam <rushikesh.s.kadam@...el.com>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Neeraj upadhyay <neeraj.iitr10@...il.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>, vineeth@...byteword.org
Subject: Re: [PATCH v2 6/8] rcuscale: Add test for using call_rcu_lazy() to
 emulate kfree_rcu()



On 7/12/2022 4:58 PM, Paul E. McKenney wrote:
> On Tue, Jul 12, 2022 at 04:27:05PM -0400, Joel Fernandes wrote:
>> Ah, with all the threads, I missed this one :(. Sorry about that.
> 
> I know that feeling...
> 
>> On Fri, Jul 8, 2022 at 7:06 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>>
>>>> Currently I added a test like the following which adds a new torture type, my
>>>> thought was to stress the new code to make sure nothing crashed or hung the
>>>> kernel. That is working well except I don't exactly understand the total-gps
>>>> print showing 0, which the other print shows 1188 GPs. I'll go dig into that
>>>> tomorrow.. thanks!
>>>>
>>>> The print shows
>>>> TREE11 ------- 1474 GPs (12.2833/s) [rcu_lazy: g0 f0x0 total-gps=0]
>>>> TREE11 no success message, 7 successful version messages
>>>
>>> Nice!!!  It is very good to see you correctly using the rcu_torture_ops
>>> facility correctly!
>>>
>>> And this could be good for your own testing, and I am happy to pull it
>>> in for that purpose (given it being fixed, having a good commit log,
>>> and so on).  After all, TREE10 is quite similar -- not part of CFLIST,
>>> but useful for certain types of focused testing.
>>>
>>> However, it would be very good to get call_rcu_lazy() testing going
>>> more generally, and in particular in TREE01 where offloading changes
>>> dynamically.  A good way to do this is to add a .call_lazy() component
>>> to the rcu_torture_ops structure, and check for it in a manner similar
>>> to that done for the .deferred_free() component.  Including adding a
>>> gp_normal_lazy module parameter.  This would allow habitual testing
>>> on a few scenarios and focused lazy testing on all of them via the
>>> --bootargs parameter.
>>
>> Ok, if you don't mind I will make this particular enhancement to the
>> torture test in a future patchset, since I kind of decided on doing v3
>> with just fixes to what I have and more testing. Certainly happy to
>> enhance these tests in a future version.
> 
> No need to gate v3 on those tests.
> 
>>> On the total-gps=0, the usual suspicion would be that the lazy callbacks
>>> never got invoked.  It looks like you were doing about a two-minute run,
>>> so maybe a longer run?  Though weren't they supposed to kick in at 15
>>> seconds or so?  Or did this value of zero come about because this run
>>> used exactly 300 grace periods?
>>
>> It was zero because it required the RCU_FLAVOR torture type, where as
>> my torture type was lazy. Adding RCU_LAZY_FLAVOR to the list fixed it
>> :)
> 
> Heh!  Then it didn't actually do any testing.  Done that as well!

Sorry to not be clear, I meant the switch-case list below, not the
torture list in rcutorture.c! It was in the rcutorture.c so was being
tested, just reporting zero gp_seq as I pointed.

/*
 * Send along grace-period-related data for rcutorture diagnostics.
 */
void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
                            unsigned long *gp_seq)
{
        switch (test_type) {
        case RCU_FLAVOR:
        case RCU_LAZY_FLAVOR:
                *flags = READ_ONCE(rcu_state.gp_flags);
                *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
                break;
        default:
                break;
        }
}
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);