From: Yury Norov <yury.norov@gmail.com>
To: Jakub Kicinski <kuba@kernel.org>,
netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: Yury Norov <yury.norov@gmail.com>,
Saeed Mahameed <saeedm@nvidia.com>,
Pawel Chmielewski <pawel.chmielewski@intel.com>,
Leon Romanovsky <leon@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Tariq Toukan <tariqt@nvidia.com>, Gal Pressman <gal@nvidia.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Heiko Carstens <hca@linux.ibm.com>,
Barry Song <baohua@kernel.org>
Subject: [PATCH 3/8] sched/topology: add for_each_numa_cpu() macro
Date: Sat, 25 Mar 2023 11:55:09 -0700 [thread overview]
Message-ID: <20230325185514.425745-4-yury.norov@gmail.com> (raw)
In-Reply-To: <20230325185514.425745-1-yury.norov@gmail.com>
for_each_cpu() is widely used in the kernel, and it's beneficial to
create a NUMA-aware version of the macro.
Recently added for_each_numa_hop_mask() works, but switching existing
codebase to it is not an easy process.
New for_each_numa_cpu() is designed to be similar to the for_each_cpu().
It allows to convert existing code to NUMA-aware as simple as adding a
hop iterator variable and passing it inside new macro. for_each_numa_cpu()
takes care of the rest.
At the moment, we have 2 users of NUMA-aware enumerators. One is
Melanox's in-tree driver, and another is Intel's in-review driver:
https://lore.kernel.org/lkml/20230216145455.661709-1-pawel.chmielewski@intel.com/
Both real-life examples follow the same pattern:
for_each_numa_hop_mask(cpus, prev, node) {
for_each_cpu_andnot(cpu, cpus, prev) {
if (cnt++ == max_num)
goto out;
do_something(cpu);
}
prev = cpus;
}
With the new macro, it would look like this:
for_each_numa_cpu(cpu, hop, node, cpu_possible_mask) {
if (cnt++ == max_num)
break;
do_something(cpu);
}
Straight conversion of existing for_each_cpu() codebase to NUMA-aware
version with for_each_numa_hop_mask() is difficult because it doesn't
take a user-provided cpu mask, and eventually ends up with open-coded
double loop. With for_each_numa_cpu() it shouldn't be a brainteaser.
Consider the NUMA-ignorant example:
cpumask_t cpus = get_mask();
int cnt = 0, cpu;
for_each_cpu(cpu, cpus) {
if (cnt++ == max_num)
break;
do_something(cpu);
}
Converting it to NUMA-aware version would be as simple as:
cpumask_t cpus = get_mask();
int node = get_node();
int cnt = 0, hop, cpu;
for_each_numa_cpu(cpu, hop, node, cpus) {
if (cnt++ == max_num)
break;
do_something(cpu);
}
The latter looks more verbose and avoids from open-coding that annoying
double loop. Another advantage is that it works with a 'hop' parameter with
the clear meaning of NUMA distance, and doesn't make people not familiar
to enumerator internals bothering with current and previous masks machinery.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
include/linux/topology.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 4a63154fa036..62a9dd8edd77 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -286,4 +286,24 @@ sched_numa_hop_mask(unsigned int node, unsigned int hops)
!IS_ERR_OR_NULL(mask); \
__hops++)
+/**
+ * for_each_numa_cpu - iterate over cpus in increasing order taking into account
+ * NUMA distances from a given node.
+ * @cpu: the (optionally unsigned) integer iterator
+ * @hop: the iterator variable, must be initialized to a desired minimal hop.
+ * @node: the NUMA node to start the search from.
+ *
+ * Requires rcu_lock to be held.
+ *
+ * Because it's implemented as double-loop, using 'break' inside the body of
+ * iterator may lead to undefined behaviour. Use 'goto' instead.
+ *
+ * Yields intersection of @mask and cpu_online_mask if @node == NUMA_NO_NODE.
+ */
+#define for_each_numa_cpu(cpu, hop, node, mask) \
+ for ((cpu) = 0, (hop) = 0; \
+ (cpu) = sched_numa_find_next_cpu((mask), (cpu), (node), &(hop)),\
+ (cpu) < nr_cpu_ids; \
+ (cpu)++)
+
#endif /* _LINUX_TOPOLOGY_H */
--
2.34.1
next prev parent reply other threads:[~2023-03-25 18:55 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-25 18:55 [PATCH 0/8] sched/topology: add for_each_numa_cpu() macro Yury Norov
2023-03-25 18:55 ` [PATCH 1/8] lib/find: add find_next_and_andnot_bit() Yury Norov
2023-03-27 10:26 ` Andy Shevchenko
2023-03-25 18:55 ` [PATCH 2/8] sched/topology: introduce sched_numa_find_next_cpu() Yury Norov
2023-03-27 10:28 ` Andy Shevchenko
2023-04-10 18:00 ` Yury Norov
2023-03-25 18:55 ` Yury Norov [this message]
2023-04-10 18:05 ` [PATCH 3/8] sched/topology: add for_each_numa_cpu() macro Yury Norov
2023-03-25 18:55 ` [PATCH 4/8] net: mlx5: switch comp_irqs_request() to using for_each_numa_cpu Yury Norov
2023-03-25 18:55 ` [PATCH 5/8] lib/cpumask: update comment to cpumask_local_spread() Yury Norov
2023-03-25 18:55 ` [PATCH 6/8] sched/topology: export sched_domains_numa_levels Yury Norov
2023-03-25 18:55 ` [PATCH 7/8] lib: add test for for_each_numa_{cpu,hop_mask}() Yury Norov
2023-03-25 18:55 ` [RFC PATCH 8/8] sched: drop for_each_numa_hop_mask() Yury Norov
2023-04-10 18:09 ` [PATCH 0/8] sched/topology: add for_each_numa_cpu() macro Yury Norov
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