From: Yury Norov <yury.norov@gmail.com>
To: linux-kernel@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Barry Song <baohua@kernel.org>, Ben Segall <bsegall@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Gal Pressman <gal@nvidia.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Haniel Bristot de Oliveira <bristot@redhat.com>,
Heiko Carstens <hca@linux.ibm.com>,
Ingo Molnar <mingo@redhat.com>,
Jacob Keller <jacob.e.keller@intel.com>,
Jakub Kicinski <kuba@kernel.org>,
Jason Gunthorpe <jgg@nvidia.com>,
Jesse Brandeburg <jesse.brandeburg@intel.com>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Juri Lelli <juri.lelli@redhat.com>,
Leon Romanovsky <leonro@nvidia.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>, Peter Lafreniere <peter@n8pjl.ca>,
Peter Zijlstra <peterz@infradead.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Saeed Mahameed <saeedm@nvidia.com>,
Steven Rostedt <rostedt@goodmis.org>,
Tariq Toukan <tariqt@nvidia.com>,
Tariq Toukan <ttoukan.linux@gmail.com>,
Tony Luck <tony.luck@intel.com>,
Valentin Schneider <vschneid@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>
Cc: Yury Norov <yury.norov@gmail.com>,
linux-crypto@vger.kernel.org, netdev@vger.kernel.org,
linux-rdma@vger.kernel.org
Subject: [PATCH 9/9] lib/cpumask: update comment for cpumask_local_spread()
Date: Fri, 20 Jan 2023 20:24:36 -0800 [thread overview]
Message-ID: <20230121042436.2661843-10-yury.norov@gmail.com> (raw)
In-Reply-To: <20230121042436.2661843-1-yury.norov@gmail.com>
Now that we have an iterator-based alternative for a very common case
of using cpumask_local_spread for all cpus in a row, it's worth to
mention that in comment to cpumask_local_spread().
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
---
lib/cpumask.c | 26 ++++++++++++++++++++++----
1 file changed, 22 insertions(+), 4 deletions(-)
diff --git a/lib/cpumask.c b/lib/cpumask.c
index 10aa15715c0d..98291b07c756 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -114,11 +114,29 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
* @i: index number
* @node: local numa_node
*
- * This function selects an online CPU according to a numa aware policy;
- * local cpus are returned first, followed by non-local ones, then it
- * wraps around.
+ * Returns online CPU according to a numa aware policy; local cpus are returned
+ * first, followed by non-local ones, then it wraps around.
*
- * It's not very efficient, but useful for setup.
+ * For those who wants to enumerate all CPUs based on their NUMA distances,
+ * i.e. call this function in a loop, like:
+ *
+ * for (i = 0; i < num_online_cpus(); i++) {
+ * cpu = cpumask_local_spread(i, node);
+ * do_something(cpu);
+ * }
+ *
+ * There's a better alternative based on for_each()-like iterators:
+ *
+ * for_each_numa_hop_mask(mask, node) {
+ * for_each_cpu_andnot(cpu, mask, prev)
+ * do_something(cpu);
+ * prev = mask;
+ * }
+ *
+ * It's simpler and more verbose than above. Complexity of iterator-based
+ * enumeration is O(sched_domains_numa_levels * nr_cpu_ids), while
+ * cpumask_local_spread() when called for each cpu is
+ * O(sched_domains_numa_levels * nr_cpu_ids * log(nr_cpu_ids)).
*/
unsigned int cpumask_local_spread(unsigned int i, int node)
{
--
2.34.1
next prev parent reply other threads:[~2023-01-21 4:25 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-21 4:24 [PATCH RESEND 0/9] sched: cpumask: improve on cpumask_local_spread() locality Yury Norov
2023-01-21 4:24 ` [PATCH 1/9] lib/find: introduce find_nth_and_andnot_bit Yury Norov
2023-01-21 4:24 ` [PATCH 2/9] cpumask: introduce cpumask_nth_and_andnot Yury Norov
2023-01-21 4:24 ` [PATCH 3/9] sched: add sched_numa_find_nth_cpu() Yury Norov
2023-02-03 0:58 ` Chen Yu
2023-02-07 5:09 ` Jakub Kicinski
2023-02-07 10:29 ` Valentin Schneider
2023-02-17 1:39 ` Yury Norov
2023-02-17 11:11 ` Andy Shevchenko
2023-02-20 19:46 ` Jakub Kicinski
2023-01-21 4:24 ` [PATCH 4/9] cpumask: improve on cpumask_local_spread() locality Yury Norov
2023-01-21 4:24 ` [PATCH 5/9] lib/cpumask: reorganize cpumask_local_spread() logic Yury Norov
2023-01-21 4:24 ` [PATCH 6/9] sched/topology: Introduce sched_numa_hop_mask() Yury Norov
2023-01-21 4:24 ` [PATCH 7/9] sched/topology: Introduce for_each_numa_hop_mask() Yury Norov
2023-01-21 4:24 ` [PATCH 8/9] net/mlx5e: Improve remote NUMA preferences used for the IRQ affinity hints Yury Norov
2023-01-21 4:24 ` Yury Norov [this message]
2023-01-22 12:57 ` [PATCH RESEND 0/9] sched: cpumask: improve on cpumask_local_spread() locality Tariq Toukan
2023-01-23 9:57 ` Valentin Schneider
2023-01-29 8:07 ` Tariq Toukan
2023-01-30 20:22 ` Jakub Kicinski
2023-02-02 17:33 ` Jakub Kicinski
2023-02-02 17:37 ` Yury Norov
2023-02-08 2:25 ` Jakub Kicinski
2023-02-08 4:20 ` patchwork-bot+netdevbpf
2023-02-08 15:39 ` [PATCH 1/1] ice: Change assigning method of the CPU affinity masks Pawel Chmielewski
[not found] ` <CAH-L+nO+KyzPSX_F0fh+9i=0rW1hoBPFTGbXc1EX+4MGYOR1kA@mail.gmail.com>
2023-02-08 16:08 ` Andy Shevchenko
2023-02-08 16:39 ` Yury Norov
2023-02-08 16:58 ` Andy Shevchenko
2023-02-08 19:11 ` kernel test robot
2023-02-09 2:41 ` Philip Li
2023-02-08 19:22 ` kernel test robot
2023-02-08 23:21 ` Jakub Kicinski
2023-02-09 5:14 ` kernel test robot
2023-02-16 14:54 ` [PATCH v2 " Pawel Chmielewski
2023-02-16 15:14 ` Andy Shevchenko
2023-02-16 15:16 ` Andy Shevchenko
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