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authorÍñigo Huguet <ihuguet@redhat.com>2022-03-15 12:18:32 +0300
committerJakub Kicinski <kuba@kernel.org>2022-03-18 22:00:35 +0300
commit046e1537a3cf0adc68fe865b5dc9a7e731cc63b3 (patch)
tree8dc25236e731b0a36a12c0816fbfcbf31ec6f035 /net/core
parente89600ebeeb14d18c0b062837a84196f72542830 (diff)
downloadlinux-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.c20
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);