> On Apr 5, 2025, at 1:23 PM, Paul E. McKenney <paul...@kernel.org> wrote:
>
> On Sat, Apr 05, 2025 at 12:30:58PM -0000, Joel Fernandes wrote:
>> Hello, Paul,
>>
>>> On Sat, 5 Apr 2025 12:26:12 GMT, "Paul E. McKenney" wrote:
>>> On Sat, Mar 29, 2025 at 07:01:42PM -0400, 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.
>>>>
>>>> Signed-off-by: Joel Fernandes <joelagn...@nvidia.com>
>>>
>>> I ran this as follows:
>>>
>>> tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 10m
>>> --configs "TREE01" --bootargs "rcutorture.ovf_cycle_mins=7" --trust-make
>>>
>>> Once I actually applied your patch, I did get this:
>>>
>>> [ 601.891042] gpwraps: 13745
>>>
>>> Which seems to indicate some testing. ;-)
>>
>> Thanks a lot for running it. I am wondering if I should check in tree.c
>> (only in
>> testing mode), if the wraps are too many and restrict testing if so.
>> Otherwise,
>> it is hard to come up with a constant that ensures the wraps are under
>> control.
>> On the other hand, since this is only for 5 minutes every 30 minutes, we can
>> leave
>> it as is and avoid the complexity.
>
> I don't (yet) see a problem with lots of wraps.
>
>>> Additional comments inline.
>>>
>>> Thanx, Paul
>>>
>>>> ---
>>>> kernel/rcu/rcu.h | 4 +++
>>>> kernel/rcu/rcutorture.c | 64 +++++++++++++++++++++++++++++++++++++++++
>>>> kernel/rcu/tree.c | 34 ++++++++++++++++++++--
>>>> kernel/rcu/tree.h | 1 +
>>>> 4 files changed, 101 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
>>>> index eed2951a4962..9a15e9701e02 100644
>>>> --- a/kernel/rcu/rcu.h
>>>> +++ b/kernel/rcu/rcu.h
>>>> @@ -572,6 +572,8 @@ void do_trace_rcu_torture_read(const char
>>>> *rcutorturename,
>>>> unsigned long c_old,
>>>> unsigned long c);
>>>> void rcu_gp_set_torture_wait(int duration);
>>>> +void rcu_set_torture_ovf_lag(unsigned long lag);
>>>> +int rcu_get_gpwrap_count(int cpu);
>>>> #else
>>>> static inline void rcutorture_get_gp_data(int *flags, unsigned long
>>>> *gp_seq)
>>>> {
>>>> @@ -589,6 +591,8 @@ void do_trace_rcu_torture_read(const char
>>>> *rcutorturename,
>>>> do { } while (0)
>>>> #endif
>>>> static inline void rcu_gp_set_torture_wait(int duration) { }
>>>> +static inline void rcu_set_torture_ovf_lag(unsigned long lag) { }
>>>> +static inline int rcu_get_gpwrap_count(int cpu) { return 0; }
>>>
>>> Very good, you did remember CONFIG_SMP=n. And yes, I did try it. ;-)
>>>
>>> But shouldn't these be function pointers in rcu_torture_ops? That way if
>>> some other flavor of RCU starts doing wrap protection for its grace-period
>>> sequence numbers, this testing can apply directly to that flavor as well.
>>
>> These are here because 'rdp' is not accessible AFAIK from rcutorture.c.
>> I could add wrappers to these and include them as pointers the a struct as
>> well.
>> But I think these will still stay to access rdp.
>
> Why not just pass in the CPU number and let the pointed-to function find
> the rdp?
You mean provide a helper from tree.c that is called in rcutorture, then helper
function returning an rdp?
If so, I can certainly do that, was just not sure if this sort of thing was ok
since nothing else in rcutorture accesses rdp directly :)
Thanks,
- Joel
>
>>> Then the pointers can simply be NULL in kernels built with CONFIG_SMP=n.
>>>
>>>> #endif
>>>> unsigned long long rcutorture_gather_gp_seqs(void);
>>>> void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t
>>>> len);
>>>> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
>>>> index 895a27545ae1..79a72e70913e 100644
>>>> --- a/kernel/rcu/rcutorture.c
>>>> +++ b/kernel/rcu/rcutorture.c
>>>> @@ -118,6 +118,9 @@ torture_param(int, nreaders, -1, "Number of RCU reader
>>>> threads");
>>>> torture_param(int, object_debug, 0, "Enable debug-object double call_rcu()
>>>> testing");
>>>> torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs
>>>> (s)");
>>>> torture_param(int, onoff_interval, 0, "Time between CPU hotplugs
>>>> (jiffies), 0=disable");
>>>> +torture_param(int, ovf_cycle_mins, 30, "Total cycle duration for ovf lag
>>>> testing (in minutes)");
>>>> +torture_param(int, ovf_active_mins, 5, "Duration for which ovf lag is
>>>> active within each cycle (in minutes)");
>>>> +torture_param(int, ovf_lag_gps, 8, "Value to set for set_torture_ovf_lag
>>>> during an active testing period.");
>>>
>>> Given that "ovf" means just "overflow", would it make sense to get a "gp"
>>> in there? Maybe just "gpwrap_..."?
>>>
>>> "What is in a name?" ;-)
>>
>> Sure, makes sense I will rename.
>
> Thank you!
>
>>> I could argue with the defaults, but I run long tests often enough that
>>> I am not worried about coverage. As long as we remember to either run
>>> long tests or specify appropriate rcutorture.ovf_cycle_mins when messing
>>> with ->gpwrap code.
>>>
>>>> torture_param(int, nocbs_nthreads, 0, "Number of NOCB toggle threads, 0 to
>>>> disable");
>>>> torture_param(int, nocbs_toggle, 1000, "Time between toggling nocb state
>>>> (ms)");
>>>> torture_param(int, preempt_duration, 0, "Preemption duration (ms), zero to
>>>> disable");
>>>> @@ -2629,6 +2632,7 @@ rcu_torture_stats_print(void)
>>>> int i;
>>>> long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
>>>> long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
>>>> + long n_gpwraps = 0;
>>>> struct rcu_torture *rtcp;
>>>> static unsigned long rtcv_snap = ULONG_MAX;
>>>> static bool splatted;
>>>> @@ -2639,6 +2643,7 @@ rcu_torture_stats_print(void)
>>>> pipesummary[i] += READ_ONCE(per_cpu(rcu_torture_count, cpu)[i]);
>>>> batchsummary[i] += READ_ONCE(per_cpu(rcu_torture_batch,
>>>> cpu)[i]);
>>>> }
>>>> + n_gpwraps += rcu_get_gpwrap_count(cpu);
>>>> }
>>>> for (i = RCU_TORTURE_PIPE_LEN; i >= 0; i--) {
>>>> if (pipesummary[i] != 0)
>>>> @@ -2672,6 +2677,7 @@ rcu_torture_stats_print(void)
>>>> pr_cont("read-exits: %ld ", data_race(n_read_exits)); // Statistic.
>>>> pr_cont("nocb-toggles: %ld:%ld\n",
>>>
>>> The "\n" on the above line needs to be deleted.
>>
>> Ok.
>>
>>>> atomic_long_read(&n_nocb_offload),
>>>> atomic_long_read(&n_nocb_deoffload));
>>>> + pr_cont("gpwraps: %ld\n", n_gpwraps);
>>>>
>>>> pr_alert("%s%s ", torture_type, TORTURE_FLAG);
>>>> if (atomic_read(&n_rcu_torture_mberror) ||
>>>> @@ -3842,6 +3848,58 @@ static int rcu_torture_preempt(void *unused)
>>>>
>>>> static enum cpuhp_state rcutor_hp;
>>>>
>>>> +static struct hrtimer ovf_lag_timer;
>>>> +static bool ovf_lag_active;
>>>
>>> Same "ovf" naming complaint as before.
>>
>> Ok.
>>
>>>> +}
>>>> +
>>>> +static int rcu_torture_ovf_lag_init(void)
>>>> +{
>>>> + if (ovf_cycle_mins <= 0 || ovf_active_mins <= 0) {
>>>> + pr_alert("rcu-torture: lag timing parameters must be positive\n");
>>>> + return -EINVAL;
>>>> + }
>>>
>>> Why not refuse to start this portion of the test when testing CONFIG_SMP=n
>>> or something other than vanilla RCU? No need to fail the test, just
>>> print something saying that this testing won't be happening.
>>
>> Got it, will do.
>
> Again, thank you!
>
>>>> +static void rcu_torture_ovf_lag_cleanup(void)
>>>> +{
>>>> + hrtimer_cancel(&ovf_lag_timer);
>>>> +
>>>> + if (ovf_lag_active) {
>>>> + rcu_set_torture_ovf_lag(0);
>>>> + ovf_lag_active = false;
>>>> + }
>>>> +}
>>>
>>> Did you try the modprobe/rmmod testing to verify that this
>>> cleans up appropriately? You could use the drgn tool to check.
>>> See tools/rcu//rcu-cbs.py for an example drgn script that digs into the
>>> rcu_data structures.
>>
>> Nice, will check!
>>
>> Will work on this and provide v2.
>
> Looking forward to it!
>
> Thanx, Paul
