On Thu, Nov 07, 2024 at 12:13:08PM +0100, Sebastian Andrzej Siewior wrote: > scf_handler() is used as a SMP function call. This function is always > invoked in IRQ-context even with forced-threading enabled. This function > frees memory which not allowed on PREEMPT_RT because the locking > underneath is using sleeping locks. > > Add a per-CPU scf_free_pool where each SMP functions adds its memory to > be freed. This memory is then freed by scftorture_invoker() on each > iteration. On the majority of invocations the number of items is less > than five. If the thread sleeps/ gets delayed the number exceed 350 but > did not reach 400 in testing. These were the spikes during testing. > The bulk free of 64 pointers at once should improve the give-back if the > list grows. The list size is ~1.3 items per invocations. > > Having one global scf_free_pool with one cleaning thread let the list > grow to over 10.000 items with 32 CPUs (again, spikes not the average) > especially if the CPU went to sleep. The per-CPU part looks like a good > compromise. > > Reported-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > Closes: https://lore.kernel.org/lkml/41619255-cdc2-4573-a360-7794fc3614f7@paulmck-laptop/ > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Nice!!! One nit at the end below. > --- > kernel/scftorture.c | 39 +++++++++++++++++++++++++++++++++++---- > 1 file changed, 35 insertions(+), 4 deletions(-) > > diff --git a/kernel/scftorture.c b/kernel/scftorture.c > index 555b3b10621fe..1268a91af5d88 100644 > --- a/kernel/scftorture.c > +++ b/kernel/scftorture.c > @@ -97,6 +97,7 @@ struct scf_statistics { > static struct scf_statistics *scf_stats_p; > static struct task_struct *scf_torture_stats_task; > static DEFINE_PER_CPU(long long, scf_invoked_count); > +static DEFINE_PER_CPU(struct llist_head, scf_free_pool); > > // Data for random primitive selection > #define SCF_PRIM_RESCHED 0 > @@ -133,6 +134,7 @@ struct scf_check { > bool scfc_wait; > bool scfc_rpc; > struct completion scfc_completion; > + struct llist_node scf_node; > }; > > // Use to wait for all threads to start. > @@ -148,6 +150,31 @@ static DEFINE_TORTURE_RANDOM_PERCPU(scf_torture_rand); > > extern void resched_cpu(int cpu); // An alternative IPI vector. > > +static void scf_add_to_free_list(struct scf_check *scfcp) > +{ > + struct llist_head *pool; > + unsigned int cpu; > + > + cpu = raw_smp_processor_id() % nthreads; > + pool = &per_cpu(scf_free_pool, cpu); > + llist_add(&scfcp->scf_node, pool); > +} > + > +static void scf_cleanup_free_list(unsigned int cpu) > +{ > + struct llist_head *pool; > + struct llist_node *node; > + struct scf_check *scfcp; > + > + pool = &per_cpu(scf_free_pool, cpu); > + node = llist_del_all(pool); > + while (node) { > + scfcp = llist_entry(node, struct scf_check, scf_node); > + node = node->next; > + kfree(scfcp); > + } > +} > + > // Print torture statistics. Caller must ensure serialization. > static void scf_torture_stats_print(void) > { > @@ -296,7 +323,7 @@ static void scf_handler(void *scfc_in) > if (scfcp->scfc_rpc) > complete(&scfcp->scfc_completion); > } else { > - kfree(scfcp); > + scf_add_to_free_list(scfcp); > } > } > > @@ -363,7 +390,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra > scfp->n_single_wait_ofl++; > else > scfp->n_single_ofl++; > - kfree(scfcp); > + scf_add_to_free_list(scfcp); > scfcp = NULL; > } > break; > @@ -391,7 +418,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra > preempt_disable(); > } else { > scfp->n_single_rpc_ofl++; > - kfree(scfcp); > + scf_add_to_free_list(scfcp); > scfcp = NULL; > } > break; > @@ -428,7 +455,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra > pr_warn("%s: Memory-ordering failure, scfs_prim: %d.\n", __func__, scfsp->scfs_prim); > atomic_inc(&n_mb_out_errs); // Leak rather than trash! > } else { > - kfree(scfcp); > + scf_add_to_free_list(scfcp); > } > barrier(); // Prevent race-reduction compiler optimizations. > } > @@ -479,6 +506,8 @@ static int scftorture_invoker(void *arg) > VERBOSE_SCFTORTOUT("scftorture_invoker %d started", scfp->cpu); > > do { > + scf_cleanup_free_list(cpu); > + > scftorture_invoke_one(scfp, &rand); > while (cpu_is_offline(cpu) && !torture_must_stop()) { > schedule_timeout_interruptible(HZ / 5); > @@ -538,6 +567,8 @@ static void scf_torture_cleanup(void) > > end: > torture_cleanup_end(); > + for (i = 0; i < nthreads; i++) > + scf_cleanup_free_list(i); It would be better for this to precede the call to torture_cleanup_end(). As soon as torture_cleanup_end() is invoked, in theory, another torture test might start. Yes, in practice, this would only matter if the next module was again scftorture and you aren't supposed to modprobe a given module until after the prior rmmod has completed, which would prevent this scf_cleanup_free_list() from interacting with the incoming instance of scftorture. But why even allow the possibility? Thanx, Paul > } > > static int __init scf_torture_init(void) > -- > 2.45.2 >
