bench_write_req.py

#!/usr/bin/env python3
#
# Test to compare performance of write requests for two qemu-img binary files.
#
# The idea of the test comes from intention to check the benefit of c8bb23cbdbe
# "qcow2: skip writing zero buffers to empty COW areas".
#
# Copyright (c) 2020 Virtuozzo International GmbH.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#


import sys
import os
import subprocess
import simplebench
from results_to_text import results_to_text


def bench_func(env, case):
    """ Handle one "cell" of benchmarking table. """
    return bench_write_req(env['qemu_img'], env['image_name'],
                           case['block_size'], case['block_offset'],
                           case['cluster_size'])


def qemu_img_pipe(*args):
    '''Run qemu-img and return its output'''
    subp = subprocess.Popen(list(args),
                            stdout=subprocess.PIPE,
                            stderr=subprocess.STDOUT,
                            universal_newlines=True)
    exitcode = subp.wait()
    if exitcode < 0:
        sys.stderr.write('qemu-img received signal %i: %s\n'
                         % (-exitcode, ' '.join(list(args))))
    return subp.communicate()[0]


def bench_write_req(qemu_img, image_name, block_size, block_offset,
                    cluster_size):
    """Benchmark write requests

    The function creates a QCOW2 image with the given path/name. Then it runs
    the 'qemu-img bench' command and makes series of write requests on the
    image clusters. Finally, it returns the total time of the write operations
    on the disk.

    qemu_img     -- path to qemu_img executable file
    image_name   -- QCOW2 image name to create
    block_size   -- size of a block to write to clusters
    block_offset -- offset of the block in clusters
    cluster_size -- size of the image cluster

    Returns {'seconds': int} on success and {'error': str} on failure.
    Return value is compatible with simplebench lib.
    """

    if not os.path.isfile(qemu_img):
        print(f'File not found: {qemu_img}')
        sys.exit(1)

    image_dir = os.path.dirname(os.path.abspath(image_name))
    if not os.path.isdir(image_dir):
        print(f'Path not found: {image_name}')
        sys.exit(1)

    image_size = 1024 * 1024 * 1024

    args_create = [qemu_img, 'create', '-f', 'qcow2', '-o',
                   f'cluster_size={cluster_size}',
                   image_name, str(image_size)]

    count = int(image_size / cluster_size) - 1
    step = str(cluster_size)

    args_bench = [qemu_img, 'bench', '-w', '-n', '-t', 'none', '-c',
                  str(count), '-s', f'{block_size}', '-o', str(block_offset),
                  '-S', step, '-f', 'qcow2', image_name]

    try:
        qemu_img_pipe(*args_create)
    except OSError as e:
        os.remove(image_name)
        return {'error': 'qemu_img create failed: ' + str(e)}

    try:
        ret = qemu_img_pipe(*args_bench)
    except OSError as e:
        os.remove(image_name)
        return {'error': 'qemu_img bench failed: ' + str(e)}

    os.remove(image_name)

    if 'seconds' in ret:
        ret_list = ret.split()
        index = ret_list.index('seconds.')
        return {'seconds': float(ret_list[index-1])}
    else:
        return {'error': 'qemu_img bench failed: ' + ret}


if __name__ == '__main__':

    if len(sys.argv) < 4:
        program = os.path.basename(sys.argv[0])
        print(f'USAGE: {program} <path to qemu-img binary file> '
              '<path to another qemu-img to compare performance with> '
              '<full or relative name for QCOW2 image to create>')
        exit(1)

    # Test-cases are "rows" in benchmark resulting table, 'id' is a caption
    # for the row, other fields are handled by bench_func.
    test_cases = [
        {
            'id': '<cluster front>',
            'block_size': 4096,
            'block_offset': 0,
            'cluster_size': 1048576
        },
        {
            'id': '<cluster middle>',
            'block_size': 4096,
            'block_offset': 524288,
            'cluster_size': 1048576
        },
        {
            'id': '<cross cluster>',
            'block_size': 1048576,
            'block_offset': 4096,
            'cluster_size': 1048576
        },
        {
            'id': '<cluster 64K>',
            'block_size': 4096,
            'block_offset': 0,
            'cluster_size': 65536
        },
    ]

    # Test-envs are "columns" in benchmark resulting table, 'id is a caption
    # for the column, other fields are handled by bench_func.
    # Set the paths below to desired values
    test_envs = [
        {
            'id': '<qemu-img binary 1>',
            'qemu_img': f'{sys.argv[1]}',
            'image_name': f'{sys.argv[3]}'
        },
        {
            'id': '<qemu-img binary 2>',
            'qemu_img': f'{sys.argv[2]}',
            'image_name': f'{sys.argv[3]}'
        },
    ]

    result = simplebench.bench(bench_func, test_envs, test_cases, count=3,
                               initial_run=False)
    print(results_to_text(result))