Add a test for read and write IOPS throttling. The test implementation
has been generated by Antigravity and Gemini with a few manual edits.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 tests/throtl/008     | 152 +++++++++++++++++++++++++++++++++++++++++++
 tests/throtl/008.out |   2 +
 2 files changed, 154 insertions(+)
 create mode 100755 tests/throtl/008
 create mode 100644 tests/throtl/008.out

diff --git a/tests/throtl/008 b/tests/throtl/008
new file mode 100755
index 000000000000..0570fc0188e0
--- /dev/null
+++ b/tests/throtl/008
@@ -0,0 +1,152 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-3.0+
+# Copyright (C) 2026 Google LLC
+#
+# Test cgroup iocost IOPS limiting.
+
+. tests/block/rc
+. common/null_blk
+. common/cgroup
+. common/fio
+
+DESCRIPTION="test cgroup iocost controller limits"
+
+requires() {
+	_have_cgroup2_controller io
+	_have_null_blk
+	_have_fio
+	_have_program bc
+	if [[ ! -e "$(_cgroup2_base_dir)/io.cost.qos" ]]; then
+		SKIP_REASONS+=("iocost controller not supported (CONFIG_BLK_CGROUP_IOCOST)")
+		return 1
+	fi
+}
+
+test() {
+	echo "Running ${TEST_NAME}"
+
+	# Create a null_blk instance
+	local null_blk_params=(
+		blocksize=4096
+		completion_nsec=0
+		memory_backed=0
+		size=1024 # MB
+		submit_queues=1
+		power=1
+	)
+	_init_null_blk nr_devices=0 queue_mode=2 &&
+	if ! _configure_null_blk nullb0 "${null_blk_params[@]}"; then
+		echo "Configuring null_blk failed"
+		return 1
+	fi
+
+	local dev_t
+	dev_t=$(</sys/block/nullb0/dev)
+	if [[ -z $dev_t ]]; then
+		echo "Failed to get major:minor for nullb0"
+		_exit_null_blk
+		return 1
+	fi
+
+	# Initialize cgroups
+	if ! _init_cgroup2; then
+		echo "Initializing cgroup2 failed"
+		_exit_null_blk
+		return 1
+	fi
+
+	# Enable io controller in the subtree
+	local deactivate_io_ctrlr=false
+	if ! grep -wq io "$(_cgroup2_base_dir)/cgroup.subtree_control"; then
+		if ! echo "+io" > "$(_cgroup2_base_dir)/cgroup.subtree_control"; then
+			echo "Failed to enable io controller on cgroup root"
+			_exit_cgroup2
+			_exit_null_blk
+			return 1
+		fi
+		deactivate_io_ctrlr=true
+	fi
+
+	if ! echo "+io" > "$CGROUP2_DIR/cgroup.subtree_control"; then
+		echo "Failed to enable io controller on $CGROUP2_DIR"
+		if [[ $deactivate_io_ctrlr == true ]]; then
+			echo "-io" > "$(_cgroup2_base_dir)/cgroup.subtree_control"
+		fi
+		_exit_cgroup2
+		_exit_null_blk
+		return 1
+	fi
+
+	# Configure iocost controller globally for the device
+	# min=100.00 max=100.00 forces vrate to be fixed at 100%
+	if ! echo "$dev_t enable=1 min=100.00 max=100.00" > "$(_cgroup2_base_dir)/io.cost.qos"; then
+		echo "Failed to configure io.cost.qos"
+		if [[ $deactivate_io_ctrlr == true ]]; then
+			echo "-io" > "$(_cgroup2_base_dir)/cgroup.subtree_control"
+		fi
+		_exit_cgroup2
+		_exit_null_blk
+		return 1
+	fi
+
+	# Limit read iops to 100 and write iops to 10.
+	# Setting rbps/wbps to 0 means they are ignored (costs calculated purely based on IOPS)
+	if ! echo "$dev_t ctrl=user model=linear rbps=0 rseqiops=100 rrandiops=100 wbps=0 wseqiops=10 wrandiops=10" > "$(_cgroup2_base_dir)/io.cost.model"; then
+		echo "Failed to configure io.cost.model"
+		echo "$dev_t enable=0" > "$(_cgroup2_base_dir)/io.cost.qos"
+		if [[ $deactivate_io_ctrlr == true ]]; then
+			echo "-io" > "$(_cgroup2_base_dir)/cgroup.subtree_control"
+		fi
+		_exit_cgroup2
+		_exit_null_blk
+		return 1
+	fi
+
+	# Create a child cgroup for test
+	local cg_name="testgrp"
+	local cg_path="$CGROUP2_DIR/$cg_name"
+	mkdir "$cg_path"
+
+	# 1. Run FIO read test
+	local -a FIO_PERF_FIELDS
+	FIO_PERF_FIELDS=("read iops")
+	if ! _fio_perf --bs=4k --rw=randread --name=read-test --filename=/dev/nullb0 \
+			--ioengine=libaio --direct=1 --iodepth=64 --time_based --runtime=10 \
+			--cgroup="blktests/$cg_name" > /dev/null 2>&1; then
+		echo "FIO read test failed"
+	else
+		local read_iops=${TEST_RUN["read iops"]}
+		if [[ -z $read_iops ]]; then
+			echo "Read IOPS is empty"
+		elif (( "$(echo "$read_iops < 90 || $read_iops > 110" | bc -l)" )); then
+			echo "Read IOPS $read_iops not in expected range [90, 110]"
+		fi
+	fi
+
+	# 2. Run FIO write test
+	FIO_PERF_FIELDS=("write iops")
+	if ! _fio_perf --bs=4k --rw=randwrite --name=write-test --filename=/dev/nullb0 \
+			--ioengine=libaio --direct=1 --iodepth=64 --time_based --runtime=10 \
+			--cgroup="blktests/$cg_name" > /dev/null 2>&1; then
+		echo "FIO write test failed"
+	else
+		local write_iops=${TEST_RUN["write iops"]}
+		if [[ -z $write_iops ]]; then
+			echo "Write IOPS is empty"
+		elif (( "$(echo "$write_iops < 8 || $write_iops > 12" | bc -l)" )); then
+			echo "Write IOPS $write_iops not in expected range [8, 12]"
+		fi
+	fi
+
+	# Clean up cgroups
+	rmdir "$cg_path"
+	if [[ $deactivate_io_ctrlr == true ]]; then
+		{ echo "-io" > "$(_cgroup2_base_dir)/cgroup.subtree_control"; } &> "${FULL}"
+	fi
+	_exit_cgroup2
+
+	# Clean up null_blk
+	_exit_null_blk
+
+	echo "Test complete"
+}
diff --git a/tests/throtl/008.out b/tests/throtl/008.out
new file mode 100644
index 000000000000..890ff7f226d1
--- /dev/null
+++ b/tests/throtl/008.out
@@ -0,0 +1,2 @@
+Running throtl/008
+Test complete