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udev/net: add IRQAffinityPolicy= option for .link files

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Add support for configuring IRQ affinity for network interfaces via
systemd .link files. For now, the new IRQAffinityPolicy= option in the [Link]
section only accepts "single", which pins all MSI IRQs to CPU 0.

This allows declarative IRQ affinity configuration for network devices
during udev processing, which is useful for optimizing network
performance on multi-core systems.

Further commits will expand the options supported by IRQAffinityPolicy=.
This commit is contained in:
Quentin Deslandes
2026-05-20 11:39:10 +02:00
parent d9600a2ac0
commit 66892d877c
5 changed files with 292 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/udev/net/link-config-gperf.gperf
+2
View File
@@ -132,6 +132,8 @@ Link.TxMaxCoalescedHighFrames, config_parse_coalesce_u32,
Link.CoalescePacketRateSampleIntervalSec, config_parse_coalesce_sec, 0, offsetof(LinkConfig, coalesce.rate_sample_interval)
/* Rx RPS CPU mask */
Link.ReceivePacketSteeringCPUMask, config_parse_rps_cpu_mask, 0, offsetof(LinkConfig, rps_cpu_mask)
/* IRQ affinity settings */
Link.IRQAffinityPolicy, config_parse_irq_affinity_policy, 0, offsetof(LinkConfig, irq_affinity_policy)
/* SR-IOV settings */
Link.SR-IOVVirtualFunctions, config_parse_sr_iov_num_vfs, 0, offsetof(LinkConfig, sr_iov_num_vfs)
SR-IOV.VirtualFunction, config_parse_sr_iov_uint32, 0, offsetof(LinkConfig, sr_iov_by_section)
src/udev/net/link-config.c
+107
View File
@@ -15,6 +15,7 @@
#include "creds-util.h"
#include "device-private.h"
#include "device-util.h"
#include "dirent-util.h"
#include "escape.h"
#include "ether-addr-util.h"
#include "ethtool-util.h"
@@ -270,6 +271,7 @@ int link_load_one(LinkConfigContext *ctx, const char *filename) {
.eee_enabled = -1,
.eee_tx_lpi_enabled = -1,
.eee_tx_lpi_timer_usec = USEC_INFINITY,
.irq_affinity_policy = _IRQ_AFFINITY_POLICY_INVALID,
};
FOREACH_ELEMENT(feature, config->features)
@@ -922,6 +924,96 @@ static int link_apply_sr_iov_config(Link *link) {
return 0;
}
static int set_irq_affinity(Link *link, unsigned irq, unsigned cpu) {
_cleanup_free_ char *affinity_path = NULL, *mask_str = NULL;
unsigned n_groups = cpu / 32;
int r;
assert(link);
if (asprintf(&affinity_path, "/proc/irq/%u/smp_affinity", irq) < 0)
return log_oom();
/* Convert CPU number to hex bitmask.
* For CPU N, set bit N (1 << N). CPUs are split by comma-separated
* 32-bits groups. To assign CPU 32, we should write 1,00000000 */
if (asprintf(&mask_str, "%x", 1U << (cpu % 32)) < 0)
return log_oom();
for (unsigned i = 0; i < n_groups; i++)
if (!strextend(&mask_str, ",00000000"))
return log_oom();
r = write_string_file(affinity_path, mask_str, WRITE_STRING_FILE_DISABLE_BUFFER);
if (r < 0)
return log_link_warning_errno(link, r, "Failed to set IRQ %u affinity to CPU %u: %m", irq, cpu);
log_link_debug(link, "Set IRQ %u affinity to CPU %u.", irq, cpu);
return 0;
}
static int link_apply_irq_affinity_single(Link *link) {
_cleanup_closedir_ DIR *dir = NULL;
int r;
assert(link);
assert(link->config);
assert(ASSERT_PTR(link->event)->dev);
r = device_opendir(link->event->dev, "device/msi_irqs", &dir);
if (r < 0) {
if (r != -ENOENT)
return log_link_error_errno(link, r, "Failed to open device/msi_irqs: %m");
log_link_debug_errno(link, r, "No MSI IRQs found, skipping IRQ affinity configuration: %m");
return 0;
}
FOREACH_DIRENT(de, dir, return log_link_error_errno(link, errno, "Failed to read directory device/msi_irqs: %m")) {
unsigned irq;
r = safe_atou(de->d_name, &irq);
if (r < 0)
return log_link_error_errno(link, r, "Failed to convert parse IRQ number: %s", de->d_name);
(void) set_irq_affinity(link, irq, /* cpu= */ 0);
}
log_link_info(link, "Applied IRQ affinity policy 'single' (pinning to CPU 0).");
return 0;
}
static int link_apply_irq_affinity(Link *link) {
_cleanup_(cpu_set_done) CPUSet effective_cpus = {};
const char *syspath;
int r;
assert(link);
assert(link->config);
assert(ASSERT_PTR(link->event)->dev);
if (link->event->event_mode != EVENT_UDEV_WORKER) {
log_link_debug(link, "Running in test mode, skipping application of IRQ affinity settings.");
return 0;
}
if (link->config->irq_affinity_policy < 0)
return 0;
r = sd_device_get_syspath(link->event->dev, &syspath);
if (r < 0)
return log_link_warning_errno(link, r, "Failed to get syspath: %m");
switch (link->config->irq_affinity_policy) {
case IRQ_AFFINITY_POLICY_SINGLE:
return link_apply_irq_affinity_single(link);
default:
assert_not_reached();
}
}
static int link_apply_rps_cpu_mask(Link *link) {
_cleanup_free_ char *mask_str = NULL;
LinkConfig *config;
@@ -1051,6 +1143,10 @@ int link_apply_config(LinkConfigContext *ctx, Link *link) {
if (r < 0)
return r;
r = link_apply_irq_affinity(link);
if (r < 0)
return r;
return link_apply_udev_properties(link);
}
@@ -1400,3 +1496,14 @@ DEFINE_CONFIG_PARSE_ENUMV(config_parse_name_policy, name_policy, NamePolicy,
DEFINE_CONFIG_PARSE_ENUMV(config_parse_alternative_names_policy, alternative_names_policy, NamePolicy,
_NAMEPOLICY_INVALID);
static const char* const irq_affinity_policy_table[_IRQ_AFFINITY_POLICY_MAX] = {
[IRQ_AFFINITY_POLICY_SINGLE] = "single",
};
DEFINE_STRING_TABLE_LOOKUP(irq_affinity_policy, IRQAffinityPolicy);
DEFINE_CONFIG_PARSE_ENUM_WITH_DEFAULT(
config_parse_irq_affinity_policy,
irq_affinity_policy,
IRQAffinityPolicy,
_IRQ_AFFINITY_POLICY_INVALID);
src/udev/net/link-config.h
+11
View File
@@ -22,6 +22,12 @@ typedef enum MACAddressPolicy {
_MAC_ADDRESS_POLICY_INVALID = -EINVAL,
} MACAddressPolicy;
typedef enum IRQAffinityPolicy {
IRQ_AFFINITY_POLICY_SINGLE,
_IRQ_AFFINITY_POLICY_MAX,
_IRQ_AFFINITY_POLICY_INVALID = -EINVAL,
} IRQAffinityPolicy;
typedef struct Link {
UdevEvent *event;
LinkConfig *config;
@@ -113,6 +119,9 @@ struct LinkConfig {
/* Rx RPS CPU mask */
CPUSet rps_cpu_mask;
/* IRQ affinity */
IRQAffinityPolicy irq_affinity_policy;
/* SR-IOV */
uint32_t sr_iov_num_vfs;
OrderedHashmap *sr_iov_by_section;
@@ -136,6 +145,7 @@ int link_get_config(LinkConfigContext *ctx, Link *link);
int link_apply_config(LinkConfigContext *ctx, Link *link);
DECLARE_STRING_TABLE_LOOKUP(mac_address_policy, MACAddressPolicy);
DECLARE_STRING_TABLE_LOOKUP(irq_affinity_policy, IRQAffinityPolicy);
/* gperf lookup function */
const struct ConfigPerfItem* link_config_gperf_lookup(const char *str, GPERF_LEN_TYPE length);
@@ -150,3 +160,4 @@ CONFIG_PARSER_PROTOTYPE(config_parse_mac_address_policy);
CONFIG_PARSER_PROTOTYPE(config_parse_name_policy);
CONFIG_PARSER_PROTOTYPE(config_parse_alternative_names_policy);
CONFIG_PARSER_PROTOTYPE(config_parse_rps_cpu_mask);
CONFIG_PARSER_PROTOTYPE(config_parse_irq_affinity_policy);
src/udev/net/test-link-config-tables.c
+1
View File
@@ -8,6 +8,7 @@ int main(int argc, char **argv) {
test_setup_logging(LOG_DEBUG);
test_table(MACAddressPolicy, mac_address_policy, MAC_ADDRESS_POLICY);
test_table(IRQAffinityPolicy, irq_affinity_policy, IRQ_AFFINITY_POLICY);
return EXIT_SUCCESS;
}
test/units/TEST-17-UDEV.irq-affinity.sh
Executable
+171
View File
@@ -0,0 +1,171 @@
#!/usr/bin/env bash
# SPDX-License-Identifier: LGPL-2.1-or-later
set -eux
set -o pipefail
# shellcheck source=test/units/util.sh
. "$(dirname "$0")"/util.sh
# Test IRQAffinityPolicy configuration
# Find a network interface with MSI IRQs (typically virtio-net in the VM)
# We need a real device to test actual IRQ affinity application
find_interface_with_msi_irqs() {
for iface in /sys/class/net/*; do
[[ -e "$iface" ]] || continue
iface_name=$(basename "$iface")
[[ "$iface_name" == "lo" ]] && continue
msi_irqs_path="$iface/device/msi_irqs"
if [[ -d "$msi_irqs_path" ]] && [[ -n "$(ls -A "$msi_irqs_path" 2>/dev/null)" ]]; then
echo "$iface_name"
return 0
fi
done
return 1
}
get_interface_irqs() {
local iface="$1"
local msi_irqs_path="/sys/class/net/$iface/device/msi_irqs"
if [[ -d "$msi_irqs_path" ]]; then
ls "$msi_irqs_path"
fi
}
check_irq_affinity() {
local irq="$1"
local expected_mask="$2"
local affinity
affinity=$(cat "/proc/irq/$irq/smp_affinity")
# Remove leading zeros and commas for comparison
affinity=$(echo "$affinity" | sed 's/^[0,]*//;s/,//g')
expected_mask=$(echo "$expected_mask" | sed 's/^[0,]*//;s/,//g')
[[ "$affinity" == "$expected_mask" ]]
}
# Test 1: Verify IRQ affinity is actually applied on a real device
if iface=$(find_interface_with_msi_irqs); then
echo "Found interface with MSI IRQs: $iface"
# Get the MAC address of the interface
mac=$(cat "/sys/class/net/$iface/address")
# Get IRQs before applying policy
irqs=$(get_interface_irqs "$iface")
echo "Interface $iface has IRQs: $irqs"
# Test 1a: test single policy
mkdir -p /run/systemd/network/
cat >/run/systemd/network/00-test-irq-affinity.link <<EOF
[Match]
MACAddress=$mac
[Link]
IRQAffinityPolicy=single
EOF
udevadm control --reload
# Trigger udev to re-apply the link configuration
udevadm trigger --action=add "/sys/class/net/$iface"
udevadm settle --timeout=30
# Verify the link file was applied
output=$(udevadm info --query property "/sys/class/net/$iface")
assert_in "ID_NET_LINK_FILE=/run/systemd/network/00-test-irq-affinity.link" "$output"
# Verify IRQ affinity was actually set to CPU 0 (mask "1")
for irq in $irqs; do
if check_irq_affinity "$irq" "1"; then
echo "IRQ $irq correctly pinned to CPU 0"
else
actual=$(cat "/proc/irq/$irq/smp_affinity")
echo "IRQ $irq affinity is '$actual', expected '1' (CPU 0)"
exit 1
fi
done
# Cleanup
rm -f /run/systemd/network/00-test-irq-affinity.link
udevadm control --reload
else
echo "No interface with MSI IRQs found, skipping actual IRQ affinity test"
fi
# Test 2: Config parsing with dummy interfaces (no MSI IRQs)
mkdir -p /run/systemd/network/
cat >/run/systemd/network/10-test-irq.link <<EOF
[Match]
Kind=dummy
MACAddress=00:50:56:c0:00:20
[Link]
Name=testirq0
IRQAffinityPolicy=single
EOF
udevadm control --reload
# Create a dummy interface
ip link add address 00:50:56:c0:00:20 type dummy
udevadm wait --settle --timeout=30 /sys/class/net/testirq0
# Check that the link file was applied
output=$(udevadm info --query property /sys/class/net/testirq0)
assert_in "ID_NET_LINK_FILE=/run/systemd/network/10-test-irq.link" "$output"
assert_in "ID_NET_NAME=testirq0" "$output"
# Test that udevadm test-builtin parses the config correctly
output=$(udevadm test-builtin --action add net_setup_link /sys/class/net/testirq0 2>&1)
assert_in "ID_NET_LINK_FILE=/run/systemd/network/10-test-irq.link" "$output"
# Test 3: Invalid policy values are rejected/warned
cat >/run/systemd/network/10-test-irq-invalid.link <<EOF
[Match]
Kind=dummy
MACAddress=00:50:56:c0:00:21
[Link]
Name=testirq1
IRQAffinityPolicy=invalid_policy
EOF
udevadm control --reload
# Create another dummy interface - invalid policy should be ignored
ip link add address 00:50:56:c0:00:21 type dummy
udevadm wait --settle --timeout=30 /sys/class/net/testirq1
# Check that the link file was still applied (invalid policy is just ignored/warned)
output=$(udevadm info --query property /sys/class/net/testirq1)
assert_in "ID_NET_LINK_FILE=/run/systemd/network/10-test-irq-invalid.link" "$output"
# Test 4: Empty policy (reset/disable)
cat >/run/systemd/network/10-test-irq-empty.link <<EOF
[Match]
Kind=dummy
MACAddress=00:50:56:c0:00:22
[Link]
Name=testirq2
IRQAffinityPolicy=
EOF
udevadm control --reload
ip link add address 00:50:56:c0:00:22 type dummy
udevadm wait --settle --timeout=30 /sys/class/net/testirq2
output=$(udevadm info --query property /sys/class/net/testirq2)
assert_in "ID_NET_LINK_FILE=/run/systemd/network/10-test-irq-empty.link" "$output"
# Cleanup
ip link del dev testirq0
ip link del dev testirq1
ip link del dev testirq2
rm -f /run/systemd/network/10-test-irq.link
rm -f /run/systemd/network/10-test-irq-invalid.link
rm -f /run/systemd/network/10-test-irq-empty.link
exit 0