diff options
author | Íñigo Huguet <ihuguet@redhat.com> | 2022-03-15 12:18:32 +0300 |
---|---|---|
committer | Jakub Kicinski <kuba@kernel.org> | 2022-03-18 22:00:35 +0300 |
commit | 046e1537a3cf0adc68fe865b5dc9a7e731cc63b3 (patch) | |
tree | 8dc25236e731b0a36a12c0816fbfcbf31ec6f035 /net/core | |
parent | e89600ebeeb14d18c0b062837a84196f72542830 (diff) | |
download | linux-046e1537a3cf0adc68fe865b5dc9a7e731cc63b3.tar.xz |
net: set default rss queues num to physical cores / 2
Network drivers can call to netif_get_num_default_rss_queues to get the
default number of receive queues to use. Right now, this default number
is min(8, num_online_cpus()).
Instead, as suggested by Jakub, use the number of physical cores divided
by 2 as a way to avoid wasting CPU resources and to avoid using both CPU
threads, but still allowing to scale for high-end processors with many
cores.
As an exception, select 2 queues for processors with 2 cores, because
otherwise it won't take any advantage of RSS despite being SMP capable.
Tested: Processor Intel Xeon E5-2620 (2 sockets, 6 cores/socket, 2
threads/core). NIC Broadcom NetXtreme II BCM57810 (10GBps). Ran some
tests with `perf stat iperf3 -R`, with parallelisms of 1, 8 and 24,
getting the following results:
- Number of queues: 6 (instead of 8)
- Network throughput: not affected
- CPU usage: utilized 0.05-0.12 CPUs more than before (having 24 CPUs
this is only 0.2-0.5% higher)
- Reduced the number of context switches by 7-50%, being more noticeable
when using a higher number of parallel threads.
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Íñigo Huguet <ihuguet@redhat.com>
Link: https://lore.kernel.org/r/20220315091832.13873-1-ihuguet@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/core')
-rw-r--r-- | net/core/dev.c | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/net/core/dev.c b/net/core/dev.c index 75bab5b0dbae..8e0cc5f2020d 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -2990,13 +2990,25 @@ EXPORT_SYMBOL(netif_set_real_num_queues); /** * netif_get_num_default_rss_queues - default number of RSS queues * - * This routine should set an upper limit on the number of RSS queues - * used by default by multiqueue devices. + * Default value is the number of physical cores if there are only 1 or 2, or + * divided by 2 if there are more. */ int netif_get_num_default_rss_queues(void) { - return is_kdump_kernel() ? - 1 : min_t(int, DEFAULT_MAX_NUM_RSS_QUEUES, num_online_cpus()); + cpumask_var_t cpus; + int cpu, count = 0; + + if (unlikely(is_kdump_kernel() || !zalloc_cpumask_var(&cpus, GFP_KERNEL))) + return 1; + + cpumask_copy(cpus, cpu_online_mask); + for_each_cpu(cpu, cpus) { + ++count; + cpumask_andnot(cpus, cpus, topology_sibling_cpumask(cpu)); + } + free_cpumask_var(cpus); + + return count > 2 ? DIV_ROUND_UP(count, 2) : count; } EXPORT_SYMBOL(netif_get_num_default_rss_queues); |