contrib: Add a script to time booting with QEMU

It is possible to use QEMU and kvm to measure the time taken by U-Boot
to hand off to Linux. Add a script to support this and print the
resulting time.

This requires a fair bit of setup; see the script for details.

Signed-off-by: Simon Glass <sjg@chromium.org>

contrib/README.rst

@@ -8,3 +8,11 @@ to the U-Boot project but are not maintained by the core developers.
 
 Note to contributors: Each item must have at least an entry in this file. Be
 sure to add the appropriate GPL-2.0-or-later SPDX tag to files.
+
+QEMU boot-timer script
+----------------------
+
+Runs qboot (or builds and starts U-Boot) and measures how long it takes to
+start Lunux. Must be run in the U-Boot source directory.
+
+File: `qemu-boot-timer.sh <../../../../contrib/qemu-boot-timer.sh>`_

contrib/qemu-boot-timer.sh

@@ -0,0 +1,93 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# .. code-block:: bash
+#    qemu-boot-timer.sh
+#
+# Runs qboot (or builds and starts U-Boot) and measures how long it takes to
+# start Linux. Must be run in the U-Boot source directory.
+#
+# See:
+#   https://stefano-garzarella.github.io/posts/2019-08-24-qemu-linux-boot-time/
+#   https://github.com/stefano-garzarella/qemu-boot-time.git
+#
+# You will need to first install tracing tools, e.g.:
+#
+# sudo apt install linux-tools-common linux-tools-generic linux-tools-`uname -r`
+#
+# and also change files and directories below
+#
+# Example usage to test qboot:
+
+# $ ./contrib/qemu-boot-timer.sh
+# qemu-system-x86_64: terminating on signal 15 from pid 3548708 (bash)
+# 1) pid 3548829
+#  qemu_init_end: 48.352996
+#  fw_start: 48.480586 (+0.12759)
+#  linux_start_boot: 66.16271 (+17.682124)
+#  Exit point 0: 66.37544 (+0.21273)
+#
+# That shows a time of 17.7 milliseconds for qboot itself
+
+# Enable this to boot qboot instead of U-Boot
+#QBOOT=-QB
+
+# Linux version to boot (read from /boot)
+version=6.8.0-60-generic
+
+# UUID of root disk within your disk image, which must be called root.img
+uuid=bcfdda4a-8249-4f40-9f0f-7c1a76b6cbe8
+
+# Set up directories to use
+DIR=/scratch/sglass/qemu-boot-time/
+PERF_DATA=perf.data
+export PERF_EXEC_PATH=/scratch/sglass/linux/tools/perf
+
+# No settings below here:
+
+# Turn on tracing in Linux
+sudo bash <<EOF
+echo 1 > /sys/kernel/debug/tracing/events/kvm/enable
+echo -1 > /proc/sys/kernel/perf_event_paranoid
+mount -o remount,mode=755 /sys/kernel/debug
+mount -o remount,mode=755 /sys/kernel/debug/tracing
+EOF
+
+# Start recording
+sleep 1
+cd $DIR
+sudo perf record -a -e kvm:kvm_entry -e kvm:kvm_pio -e sched:sched_process_exec \
+	-o $PERF_DATA 2> /tmp/trace.log &
+PERF_PID=$!
+
+# Run QEWU with qboot or U-Boot (builds U-Boot automatically)
+sleep 1
+cd ~/u
+./scripts/build-qemu -a x86 ${QBOOT} -rs -v -K /boot/vmlinuz-${version} \
+	-k -d root.img -I /boot/initrd.img-${version} -C -U ${uuid} -s \
+	2>&1 >/tmp/qemu.log &
+
+while [[ -z "$QEMU_PID" ]]; do
+	QEMU_PID=$(pgrep qemu-system-x86)
+done
+
+# Wait for it to boot
+sleep 5
+
+# Kill QEMU and the perf process
+kill $QEMU_PID
+sleep 1
+
+kill $PERF_PID
+wait $PERF_PID
+
+# Adjust permissions on perf data
+cd $DIR
+sudo chmod a+r $PERF_DATA
+
+# Generate the Python script to permit access to the trace
+perf script -g python 2>/dev/null
+
+# Run our script which looks for timing points and prints the results
+perf script -s ~/perf-script.py -s ${DIR}/perf-script/qemu-perf-script.py \
+	-i $PERF_DATA