libct/cg/fs2: set per-device io weight if available

libcontainer/cgroups/fs/blkio.go

@@ -41,11 +41,15 @@ func (s *BlkioGroup) Set(path string, r *configs.Resources) error {
 		}
 	}
 	for _, wd := range r.BlkioWeightDevice {
-		if err := cgroups.WriteFile(path, s.weightDeviceFilename, wd.WeightString()); err != nil {
-			return err
+		if wd.Weight != 0 {
+			if err := cgroups.WriteFile(path, s.weightDeviceFilename, wd.WeightString()); err != nil {
+				return err
+			}
 		}
-		if err := cgroups.WriteFile(path, "blkio.leaf_weight_device", wd.LeafWeightString()); err != nil {
-			return err
+		if wd.LeafWeight != 0 {
+			if err := cgroups.WriteFile(path, "blkio.leaf_weight_device", wd.LeafWeightString()); err != nil {
+				return err
+			}
 		}
 	}
 	for _, td := range r.BlkioThrottleReadBpsDevice {

libcontainer/cgroups/fs2/io.go

@@ -4,6 +4,8 @@ package fs2
 
 import (
 	"bufio"
+	"bytes"
+	"fmt"
 	"os"
 	"strconv"
 	"strings"
@@ -16,32 +18,64 @@ import (
 
 func isIoSet(r *configs.Resources) bool {
 	return r.BlkioWeight != 0 ||
+		len(r.BlkioWeightDevice) > 0 ||
 		len(r.BlkioThrottleReadBpsDevice) > 0 ||
 		len(r.BlkioThrottleWriteBpsDevice) > 0 ||
 		len(r.BlkioThrottleReadIOPSDevice) > 0 ||
 		len(r.BlkioThrottleWriteIOPSDevice) > 0
 }
 
+// bfqDeviceWeightSupported checks for per-device BFQ weight support (added
+// in kernel v5.4, commit 795fe54c2a8) by reading from "io.bfq.weight".
+func bfqDeviceWeightSupported(bfq *os.File) bool {
+	if bfq == nil {
+		return false
+	}
+	_, _ = bfq.Seek(0, 0)
+	buf := make([]byte, 32)
+	_, _ = bfq.Read(buf)
+	// If only a single number (default weight) if read back, we have older kernel.
+	_, err := strconv.ParseInt(string(bytes.TrimSpace(buf)), 10, 64)
+	return err != nil
+}
+
 func setIo(dirPath string, r *configs.Resources) error {
 	if !isIoSet(r) {
 		return nil
 	}
 
+	// If BFQ IO scheduler is available, use it.
+	var bfq *os.File
+	if r.BlkioWeight != 0 || len(r.BlkioWeightDevice) > 0 {
+		var err error
+		bfq, err = cgroups.OpenFile(dirPath, "io.bfq.weight", os.O_RDWR)
+		if err == nil {
+			defer bfq.Close()
+		} else if !os.IsNotExist(err) {
+			return err
+		}
+	}
+
 	if r.BlkioWeight != 0 {
-		filename := "io.bfq.weight"
-		if err := cgroups.WriteFile(dirPath, filename,
-			strconv.FormatUint(uint64(r.BlkioWeight), 10)); err != nil {
-			// if io.bfq.weight does not exist, then bfq module is not loaded.
-			// Fallback to use io.weight with a conversion scheme
-			if !os.IsNotExist(err) {
+		if bfq != nil { // Use BFQ.
+			if _, err := bfq.WriteString(strconv.FormatUint(uint64(r.BlkioWeight), 10)); err != nil {
 				return err
 			}
+		} else {
+			// Fallback to io.weight with a conversion scheme.
 			v := cgroups.ConvertBlkIOToIOWeightValue(r.BlkioWeight)
 			if err := cgroups.WriteFile(dirPath, "io.weight", strconv.FormatUint(v, 10)); err != nil {
 				return err
 			}
 		}
 	}
+	if bfqDeviceWeightSupported(bfq) {
+		for _, wd := range r.BlkioWeightDevice {
+			if _, err := bfq.WriteString(wd.WeightString() + "\n"); err != nil {
+				return fmt.Errorf("setting device weight %q: %w", wd.WeightString(), err)
+			}
+		}
+	}
 	for _, td := range r.BlkioThrottleReadBpsDevice {
 		if err := cgroups.WriteFile(dirPath, "io.max", td.StringName("rbps")); err != nil {
 			return err

tests/integration/cgroups.bats

@@ -150,6 +150,43 @@ function setup() {
 	fi
 }
 
+@test "runc run (per-device io weight for bfq)" {
+	requires root # to create a loop device
+
+	dd if=/dev/zero of=backing.img bs=4096 count=1
+	dev=$(losetup --find --show backing.img) || skip "unable to create a loop device"
+
+	# See if BFQ scheduler is available.
+	if ! { grep -qw bfq "/sys/block/${dev#/dev/}/queue/scheduler" &&
+		echo bfq >"/sys/block/${dev#/dev/}/queue/scheduler"; }; then
+		losetup -d "$dev"
+		skip "BFQ scheduler not available"
+	fi
+
+	set_cgroups_path
+
+	IFS=$' \t:' read -r major minor <<<"$(lsblk -nd -o MAJ:MIN "$dev")"
+	update_config '	  .linux.devices += [{path: "'"$dev"'", type: "b", major: '"$major"', minor: '"$minor"'}]
+			| .linux.resources.blockIO.weight |= 333
+			| .linux.resources.blockIO.weightDevice |= [
+				{ major: '"$major"', minor: '"$minor"', weight: 444 }
+			]'
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_dev_weight
+	[ "$status" -eq 0 ]
+
+	# The loop device itself is no longer needed.
+	losetup -d "$dev"
+
+	if [ "$CGROUP_UNIFIED" = "yes" ]; then
+		file="io.bfq.weight"
+	else
+		file="blkio.bfq.weight_device"
+	fi
+	weights=$(get_cgroup_value $file)
+	[[ "$weights" == *"default 333"* ]]
+	[[ "$weights" == *"$major:$minor 444"* ]]
+}
+
 @test "runc run (cgroup v2 resources.unified only)" {
 	requires root cgroups_v2
 

tests/integration/helpers.bash

@@ -168,10 +168,9 @@ function set_cgroups_path() {
 	update_config '.linux.cgroupsPath |= "'"${OCI_CGROUPS_PATH}"'"' "$bundle"
 }
 
-# Helper to check a value in cgroups.
-function check_cgroup_value() {
+# Get a value from a cgroup file.
+function get_cgroup_value() {
 	local source=$1
-	local expected=$2
 	local cgroup var current
 
 	if [ "x$CGROUP_UNIFIED" = "xyes" ]; then
@@ -181,9 +180,15 @@ function check_cgroup_value() {
 		var=CGROUP_${var^^}_BASE_PATH # variable name (e.g. CGROUP_MEMORY_BASE_PATH)
 		eval cgroup=\$${var}${REL_CGROUPS_PATH}
 	fi
+	cat $cgroup/$source
+}
+
+# Helper to check a if value in a cgroup file matches the expected one.
+function check_cgroup_value() {
+	local current
+	current="$(get_cgroup_value $1)"
+	local expected=$2
 
-	current=$(cat $cgroup/$source)
-	echo $cgroup/$source
 	echo "current" $current "!?" "$expected"
 	[ "$current" = "$expected" ]
 }