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net: add /proc/sys/net/core/txq_reselection_ms control

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Add a new sysctl to control how often a queue reselection
can happen even if a flow has a persistent queue of skbs
in a Qdisc or NIC queue.

A value of zero means the feature is disabled.

Default is 1000 (1 second).

This sysctl is used in the following patch.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251013152234.842065-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2025-10-13 15:22:33 +00:00 • committed by Jakub Kicinski
parent d365c9bca3
commit 2ddef3462b
4 changed files with 26 additions and 0 deletions
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17
Documentation/admin-guide/sysctl/net.rst
View file

@ -406,6 +406,23 @@ to SOCK_TXREHASH_DEFAULT (i. e. not overridden by setsockopt).
If set to 1 (default), hash rethink is performed on listening socket.
If set to 0, hash rethink is not performed.
txq_reselection_ms
------------------
Controls how often (in ms) a busy connected flow can select another tx queue.
A resection is desirable when/if user thread has migrated and XPS
would select a different queue. Same can occur without XPS
if the flow hash has changed.
But switching txq can introduce reorders, especially if the
old queue is under high pressure. Modern TCP stacks deal
well with reorders if they happen not too often.
To disable this feature, set the value to 0.
Default : 1000
gro_normal_batch
----------------

1
include/net/netns/core.h
View file

@ -13,6 +13,7 @@ struct netns_core {
struct ctl_table_header *sysctl_hdr;
int sysctl_somaxconn;
int sysctl_txq_reselection;
int sysctl_optmem_max;
u8 sysctl_txrehash;
u8 sysctl_tstamp_allow_data;

1
net/core/net_namespace.c
View file

@ -395,6 +395,7 @@ static __net_init void preinit_net_sysctl(struct net *net)
net->core.sysctl_optmem_max = 128 * 1024;
net->core.sysctl_txrehash = SOCK_TXREHASH_ENABLED;
net->core.sysctl_tstamp_allow_data = 1;
net->core.sysctl_txq_reselection = msecs_to_jiffies(1000);
}
/* init code that must occur even if setup_net() is not called. */

7
net/core/sysctl_net_core.c
View file

@ -667,6 +667,13 @@ static struct ctl_table netns_core_table[] = {
.extra2 = SYSCTL_ONE,
.proc_handler = proc_dou8vec_minmax,
},
{
.procname = "txq_reselection_ms",
.data = &init_net.core.sysctl_txq_reselection,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_ms_jiffies,
},
{
.procname = "tstamp_allow_data",
.data = &init_net.core.sysctl_tstamp_allow_data,