On Mon, Jul 22, 2024 at 07:07:35PM +0530, [email protected] wrote:
> From: "Paul E. McKenney" <[email protected]>
>
> Currently, the CSD-lock diagnostics in CONFIG_CSD_LOCK_WAIT_DEBUG=y
> kernels are emitted at five-second intervals. Although this has proven
> to be a good time interval for the first diagnostic, if the target CPU
> keeps interrupts disabled for way longer than five seconds, the ratio
> of useful new information to pointless repetition increases considerably.
>
> Therefore, back off the time period for repeated reports of the same
> incident, increasing linearly with the number of reports and logarithmicly
> with the number of online CPUs.
>
> [ paulmck: Apply Dan Carpenter feedback. ]
>
> Signed-off-by: Paul E. McKenney <[email protected]>
> Cc: Imran Khan <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Leonardo Bras <[email protected]>
> Cc: "Peter Zijlstra (Intel)" <[email protected]>
> Cc: Rik van Riel <[email protected]>
> Reviewed-by: Rik van Riel <[email protected]>
> Signed-off-by: Neeraj Upadhyay <[email protected]>
> ---
> kernel/smp.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 9385cc05de53..dfcde438ef63 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -225,7 +225,7 @@ bool csd_lock_is_stuck(void)
> * the CSD_TYPE_SYNC/ASYNC types provide the destination CPU,
> * so waiting on other types gets much less information.
> */
> -static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64
> *ts1, int *bug_id)
> +static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64
> *ts1, int *bug_id, unsigned long *nmessages)
> {
> int cpu = -1;
> int cpux;
> @@ -248,7 +248,9 @@ static bool csd_lock_wait_toolong(call_single_data_t
> *csd, u64 ts0, u64 *ts1, in
> ts2 = sched_clock();
> /* How long since we last checked for a stuck CSD lock.*/
> ts_delta = ts2 - *ts1;
> - if (likely(ts_delta <= csd_lock_timeout_ns || csd_lock_timeout_ns == 0))
> + if (likely(ts_delta <= csd_lock_timeout_ns * (*nmessages + 1) *
> + (!*nmessages ? 1 : (ilog2(num_online_cpus()) / 2
> + 1)) ||
> + csd_lock_timeout_ns == 0))
I think this is a nice change.
OTOH above condition is quite hard to read IMHO.
IIUC you want, for csd_lock_timeout_ns 5s, and num_online_cpus = 64
1st message: after 5s
2nd message: after 5 * 2 * (6 / 2 + 1) = 10 * 4 = 40s
3rd message: after 5 * 3 * 4 = 60s
...
Is that correct?
I think this could be achieved with:
/* How long since we last checked for a stuck CSD lock.*/
ts_delta = ts2 - *ts1;
+ if (*nmessages)
+ csd_lock_timeout_ns *= (*nmessages + 1) *
(ilog2(num_online_cpus()) / 2 + 1)
if (likely(ts_delta <= csd_lock_timeout_ns || csd_lock_timeout_ns == 0))
return false;
Does that look better?
Thanks!
Leo
>
> firsttime = !*bug_id;
> @@ -265,6 +267,7 @@ static bool csd_lock_wait_toolong(call_single_data_t
> *csd, u64 ts0, u64 *ts1, in
> pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %lld
> ns for CPU#%02d %pS(%ps).\n",
> firsttime ? "Detected" : "Continued", *bug_id,
> raw_smp_processor_id(), (s64)ts_delta,
> cpu, csd->func, csd->info);
> + (*nmessages)++;
> if (firsttime)
> atomic_inc(&n_csd_lock_stuck);
> /*
> @@ -305,12 +308,13 @@ static bool csd_lock_wait_toolong(call_single_data_t
> *csd, u64 ts0, u64 *ts1, in
> */
> static void __csd_lock_wait(call_single_data_t *csd)
> {
> + unsigned long nmessages = 0;
> int bug_id = 0;
> u64 ts0, ts1;
>
> ts1 = ts0 = sched_clock();
> for (;;) {
> - if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id))
> + if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id, &nmessages))
> break;
> cpu_relax();
> }
> --
> 2.40.1
>
