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From:   SeongJae Park <sj@kernel.org>
To:     SeongJae Park <sj@kernel.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/5] selftests/damon: add a test for update_schemes_tried_regions sysfs command
Date:   Tue, 12 Dec 2023 19:22:18 +0000
Message-Id: <20231212192218.54095-1-sj@kernel.org>
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In-Reply-To: <20231212191206.52917-5-sj@kernel.org>
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This and fifth patch of this patchset may not cleanly applicable, since those
are made on top of my out-of-tree experimental changes.  I will rebase these
and send v2.  Sorry for the noise.


Thanks,
SJ

On 2023-12-12T19:12:05+00:00 SeongJae Park <sj@kernel.org> wrote:

> Add a selftest for verifying the accuracy of DAMON's access monitoring
> functionality.  The test starts a program of artificial access pattern,
> monitor the access pattern using DAMON, and check if DAMON finds
> expected amount of hot data region (working set size) with only
> acceptable error rate.
> 
> Note that the acceptable error rate is set with only naive assumptions
> and small number of tests.  Hence failures of the test may not always
> mean DAMON is broken.  Rather than that, those could be a signal to
> better understand the real accuracy level of DAMON in wider
> environments.  Based on further finding, we could optimize DAMON or
> adjust the expectation of the test.
> 
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>  tools/testing/selftests/damon/Makefile        |  2 +
>  tools/testing/selftests/damon/access_memory.c | 41 ++++++++++++++
>  ...te_schemes_tried_regions_wss_estimation.py | 55 +++++++++++++++++++
>  3 files changed, 98 insertions(+)
>  create mode 100644 tools/testing/selftests/damon/access_memory.c
>  create mode 100755 tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py
> 
> diff --git a/tools/testing/selftests/damon/Makefile b/tools/testing/selftests/damon/Makefile
> index d2105d41ea25..1363987709c6 100644
> --- a/tools/testing/selftests/damon/Makefile
> +++ b/tools/testing/selftests/damon/Makefile
> @@ -4,6 +4,7 @@
>  TEST_GEN_FILES += huge_count_read_write
>  TEST_GEN_FILES += dbgfs_target_ids_read_before_terminate_race
>  TEST_GEN_FILES += dbgfs_target_ids_pid_leak
> +TEST_GEN_FILES += access_memory
>  
>  TEST_FILES = _chk_dependency.sh _debugfs_common.sh
>  TEST_PROGS = debugfs_attrs.sh debugfs_schemes.sh debugfs_target_ids.sh
> @@ -11,6 +12,7 @@ TEST_PROGS += debugfs_empty_targets.sh debugfs_huge_count_read_write.sh
>  TEST_PROGS += debugfs_duplicate_context_creation.sh
>  TEST_PROGS += debugfs_rm_non_contexts.sh
>  TEST_PROGS += sysfs.sh sysfs_update_removed_scheme_dir.sh
> +TEST_PROGS += sysfs_update_schemes_tried_regions_wss_estimation.py
>  TEST_PROGS += reclaim.sh lru_sort.sh
>  TEST_PROGS += dbgfs_target_ids_read_before_terminate_race.sh
>  TEST_PROGS += dbgfs_target_ids_pid_leak.sh
> diff --git a/tools/testing/selftests/damon/access_memory.c b/tools/testing/selftests/damon/access_memory.c
> new file mode 100644
> index 000000000000..585a2fa54329
> --- /dev/null
> +++ b/tools/testing/selftests/damon/access_memory.c
> @@ -0,0 +1,41 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Artificial memory access program for testing DAMON.
> + */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <time.h>
> +
> +int main(int argc, char *argv[])
> +{
> +	char **regions;
> +	clock_t start_clock;
> +	int nr_regions;
> +	int sz_region;
> +	int access_time_ms;
> +	int i;
> +
> +	if (argc != 4) {
> +		printf("Usage: %s <number> <size (bytes)> <time (ms)>\n",
> +				argv[0]);
> +		return -1;
> +	}
> +
> +	nr_regions = atoi(argv[1]);
> +	sz_region = atoi(argv[2]);
> +	access_time_ms = atoi(argv[3]);
> +
> +	regions = malloc(sizeof(*regions) * nr_regions);
> +	for (i = 0; i < nr_regions; i++)
> +		regions[i] = malloc(sz_region);
> +
> +	for (i = 0; i < nr_regions; i++) {
> +		start_clock = clock();
> +		while ((clock() - start_clock) * 1000 / CLOCKS_PER_SEC <
> +				access_time_ms)
> +			memset(regions[i], i, 1024 * 1024 * 10);
> +	}
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py b/tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py
> new file mode 100755
> index 000000000000..cdbf19b442c9
> --- /dev/null
> +++ b/tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py
> @@ -0,0 +1,55 @@
> +#!/usr/bin/env python3
> +# SPDX-License-Identifier: GPL-2.0
> +
> +import subprocess
> +import time
> +
> +import _damon_sysfs
> +
> +def main():
> +    # access two 10 MiB memory regions, 2 second per each
> +    sz_region = 10 * 1024 * 1024
> +    proc = subprocess.Popen(['./access_memory', '2', '%d' % sz_region, '2000'])
> +    kdamonds = _damon_sysfs.Kdamonds([_damon_sysfs.Kdamond(
> +            contexts=[_damon_sysfs.DamonCtx(
> +                ops='vaddr',
> +                targets=[_damon_sysfs.DamonTarget(pid=proc.pid)],
> +                schemes=[_damon_sysfs.Damos(
> +                    access_pattern=_damon_sysfs.DamosAccessPattern(
> +                        # >= 25% access rate, >= 200ms age
> +                        nr_accesses=[5, 20], age=[2, 2**64 - 1]))] # schemes
> +                )] # contexts
> +            )]) # kdamonds
> +
> +    err = kdamonds.start()
> +    if err != None:
> +        print('kdmaond start failed: %s' % err)
> +        exit(1)
> +
> +    wss_collected = []
> +    while proc.poll() == None:
> +        time.sleep(0.1)
> +        err = kdamonds.kdamonds[0].update_schemes_tried_bytes()
> +        if err != None:
> +            print('tried bytes update failed: %s' % err)
> +            exit(1)
> +
> +        wss_collected.append(
> +                kdamonds.kdamonds[0].contexts[0].schemes[0].tried_bytes)
> +
> +    wss_collected.sort()
> +    acceptable_error_rate = 0.2
> +    for percentile in [50, 75]:
> +        sample = wss_collected[int(len(wss_collected) * percentile / 100)]
> +        error_rate = abs(sample - sz_region) / sz_region
> +        print('%d-th percentile (%d) error %f' %
> +                (percentile, sample, error_rate))
> +        if error_rate > acceptable_error_rate:
> +            print('the error rate is not acceptable (> %f)' %
> +                    acceptable_error_rate)
> +            print('samples are as below')
> +            print('\n'.join(['%d' % wss for wss in wss_collected]))
> +            exit(1)
> +
> +if __name__ == '__main__':
> +    main()
> -- 
> 2.34.1