Messages in this thread | | | Subject | Re: [PATCH] sched,topology: Update sched topology atomically | From | "" <> | Date | Mon, 11 Apr 2022 17:01:10 +0800 |
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Hi, Valentin,
Thanks a lot for review!
On Fri, 2022-04-08 at 17:52 +0100, Valentin Schneider wrote: > > Hi, > > On 06/04/22 15:01, Huang Ying wrote: > > When Peter Zijlstra reviewed commit 0fb3978b0aac ("sched/numa: Fix > > NUMA topology for systems with CPU-less nodes") [1], he pointed out > > that sched_domains_numa_distance and sched_domains_numa_masks are made > > separate RCU variables. That could go side-ways if there were a > > function using both, although there isn't for now. > > > > So we update sched_domains_numa_distance and sched_domains_numa_masks > > and some other related sched topology parameters atomically to address > > the potential issues. > > > > [1] https://lkml.kernel.org/r/20220214121553.582248-1- > > ying.huang@intel.com > > > > I had to re-acquaint myself with [1], but AFAICT this looks mostly > OK. Have some nits/comments below, I haven't actually tested this yet as > I'm still setting stuff up over here... > > > Signed-off-by: "Huang, Ying" <ying.huang@intel.com> > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > > Cc: Valentin Schneider <valentin.schneider@arm.com> > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: Mel Gorman <mgorman@suse.de> > > Cc: Rik van Riel <riel@surriel.com> > > Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> > > --- > > kernel/sched/fair.c | 47 ++++++--- > > kernel/sched/sched.h | 14 ++- > > kernel/sched/topology.c | 223 +++++++++++++++++++--------------------- > > 3 files changed, 151 insertions(+), 133 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index d4bd299d67ab..546e7347fafc 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -1294,17 +1294,22 @@ static unsigned long score_nearby_nodes(struct > > task_struct *p, int nid, > > int lim_dist, bool task) > > { > > unsigned long score = 0; > > - int node, max_dist; > > + int node, max_dist, type; > > + struct sched_numa_topology *topology; > > + > > + rcu_read_lock(); > > + topology = rcu_dereference(sched_numa_topology); > > + type = topology->type; > > + max_dist = topology->max_distance; > > + rcu_read_unlock(); > > > > One thing worth pointing out, the NUMA topology type *wasn't* RCU protected > previously, which I think we've been wanting since > > 0083242c9375 ("sched/topology: Skip updating masks for non-online nodes") > > (before then the topology was init'd once-and-for-all). > > Another thing; this pattern is now repeated a handful of times in fair.c, > what about bundling it up? As a bonus it lets us keep the definition of > struct sched_numa_topology internal to topology.c: > > void sched_fetch_numa_topology(int *type int *max_distance) > { > struct sched_numa_topology __rcu *topology; > > rcu_read_lock(); > topology = rcu_dereference(sched_numa_topology); > > if (type) > *type = topology->type; > > if (max_distance) > *max_distance = topology->max_distance; > > > rcu_read_unlock(); > } >
This looks good. Will use it in the next version. Thanks!
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > > index 810750e62118..19523b23034f 100644 > > --- a/kernel/sched/topology.c > > +++ b/kernel/sched/topology.c > > @@ -1483,14 +1483,10 @@ static void claim_allocations(int cpu, struct > > sched_domain *sd) > > } > > > > #ifdef CONFIG_NUMA > > -enum numa_topology_type sched_numa_topology_type; > > +struct sched_numa_topology default_numa_topology; > > Shouldn't this be static?
Yes. Will change it in the next version.
> > +struct sched_numa_topology *sched_numa_topology = > > &default_numa_topology; > > This should also be __rcu (sparse should complain about this)
Yes. Will change it in the next version.
> > > > -static int sched_domains_numa_levels; > > static int sched_domains_curr_level; > > - > > -int sched_max_numa_distance; > > -static int *sched_domains_numa_distance; > > -static struct cpumask ***sched_domains_numa_masks; > > #endif > > > > /* > > > +static void sched_numa_topology_switch(struct sched_numa_topology > > *topology, > > + struct sched_domain_topology_level > > *tl) > > +{ > > + struct sched_numa_topology *old_topology = sched_numa_topology; > > + struct sched_domain_topology_level *old_tl = > > sched_domain_topology; > > + > > + rcu_assign_pointer(sched_numa_topology, topology); > > + sched_domain_topology = tl; > > + > > + if (old_topology == &default_numa_topology) > > + return; > > + > > + init_rcu_head(&old_topology->rcu); > > I'm not familiar with this and I can find only a handful of users, should > we be doing that for struct sched_domain?
Per my understanding, this is for debug and we should call it before call_rcu(). Copying Paul for confirmation.
> > > + call_rcu(&old_topology->rcu, sched_numa_topology_free_rcu); > > + kfree(old_tl); > > +} > > > > #define NR_DISTANCE_VALUES (1 << DISTANCE_BITS) > > > > void sched_init_numa(int offline_node) > > { > > struct sched_domain_topology_level *tl; > > - unsigned long *distance_map; > > + unsigned long *distance_map = NULL; > > int nr_levels = 0; > > int i, j; > > - int *distances; > > - struct cpumask ***masks; > > + struct sched_numa_topology *topology; > > + > > + topology = kzalloc(sizeof(*topology), GFP_KERNEL); > > + if (!topology) > > + goto err; > > > > /* > > * O(nr_nodes^2) deduplicating selection sort -- in order to find > > the > > > + return; > > +err: > > I was expecting the "usual" multi-label setup, but this seems to be working > too - though not in the most obvious way ;)
OK. Will try to convert it to multi-label.
> > > + bitmap_free(distance_map); > > + sched_numa_topology_free(topology); > > + sched_numa_topology_switch(&default_numa_topology, > > + sched_domain_topology_default); > > } > > > > /* > > @@ -1981,7 +1977,6 @@ void sched_update_numa(int cpu, bool online) > > if (cpumask_weight(cpumask_of_node(node)) != 1) > > return; > > > > - sched_reset_numa(); > > sched_init_numa(online ? NUMA_NO_NODE : node); > > } > > > > @@ -1990,14 +1985,15 @@ void sched_domains_numa_masks_set(unsigned int > > cpu) > > int node = cpu_to_node(cpu); > > int i, j; > > > > - for (i = 0; i < sched_domains_numa_levels; i++) { > > + for (i = 0; i < sched_numa_topology->nr_levels; i++) { > > for (j = 0; j < nr_node_ids; j++) { > > if (!node_state(j, N_CPU)) > > continue; > > > > /* Set ourselves in the remote node's masks */ > > - if (node_distance(j, node) <= > > sched_domains_numa_distance[i]) > > - cpumask_set_cpu(cpu, > > sched_domains_numa_masks[i][j]); > > + if (node_distance(j, node) <= > > + sched_numa_topology->distances[i]) > > + cpumask_set_cpu(cpu, sched_numa_topology- > > >masks[i][j]); > will be 0 > I'm guessing the assumption here is that this is done in > sched_cpu_{de,}activate(), so we have the hotplug lock and so the masks are > stable... Should we sprinkle in a lockdep_assert_cpus_held() for good > measure? > > Having a second look at this, I think the same applies to your change to > sd_numa_mask() - those end up used in the domain rebuild which itself might > be deferred cpuset_hotplug_work, but that should still hold the hotplug > lock...
Yes. hotplug lock needs to be held in these places. Will add lockdep_assert_cpus_held() in necessary places.
> > } > > } > > } > > @@ -2006,10 +2002,10 @@ void sched_domains_numa_masks_clear(unsigned int > > cpu) > > { > > int i, j; > > > > - for (i = 0; i < sched_domains_numa_levels; i++) { > > + for (i = 0; i < sched_numa_topology->nr_levels; i++) { > > for (j = 0; j < nr_node_ids; j++) { > > - if (sched_domains_numa_masks[i][j]) > > - cpumask_clear_cpu(cpu, > > sched_domains_numa_masks[i][j]); > > + if (sched_numa_topology->masks[i][j]) > > + cpumask_clear_cpu(cpu, > > sched_numa_topology->masks[i][j]); > > } > > } > > } > > @@ -2025,22 +2021,19 @@ void sched_domains_numa_masks_clear(unsigned int > > cpu) > > int sched_numa_find_closest(const struct cpumask *cpus, int cpu) > > { > > int i, j = cpu_to_node(cpu), found = nr_cpu_ids; > > - struct cpumask ***masks; > > + struct sched_numa_topology *topology; > > > > rcu_read_lock(); > > - masks = rcu_dereference(sched_domains_numa_masks); > > - if (!masks) > > - goto unlock; > > - for (i = 0; i < sched_domains_numa_levels; i++) { > > - if (!masks[i][j]) > > + topology = rcu_dereference(sched_numa_topology); > > + for (i = 0; i < topology->nr_levels; i++) { > > + if (!topology->masks[i][j]) > > If I got default_numa_topology right and it's meant to be static, > sched_numa_topology->masks can still be NULL, but here this would be gated > by nr_levels being 0... Did I get that right?
Yes. nr_levels in default_numa_topology is 0.
> > > break; > > - cpu = cpumask_any_and(cpus, masks[i][j]); > > + cpu = cpumask_any_and(cpus, topology->masks[i][j]); > > if (cpu < nr_cpu_ids) { > > found = cpu; > > break; > > } > > } > > -unlock: > > rcu_read_unlock(); > > > > return found; > > -- > > 2.30.2 >
Best Regards, Huang, Ying
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