Re: [dpdk-dev] [PATCH v5] pflock: implementation of phase-fair reader writer locks

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> This is a new type of reader-writer lock that provides better fairness
> guarantees which better suited for typical DPDK applications.
> A pflock has two ticket pools, one for readers and one for writers.
> 
> Phase fair reader writer locks ensure that neither reader nor writer will be
> starved. Neither reader or writer are preferred, they execute in alternating
> phases. All operations of the same type (reader or writer) that acquire the
> lock are handled in FIFO order.  Write operations are exclusive, and multiple
> read operations can be run together (until a write arrives).
> 
> A similar implementation is in Concurrency Kit package in FreeBSD.
> For more information see:
>    "Reader-Writer Synchronization for Shared-Memory Multiprocessor
>     Real-Time Systems",
>     http://www.cs.unc.edu/~anderson/papers/ecrts09b.pdf
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Looks good.
Acked-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

One question below

> ---
> v5 - cleanup typos in the lock code comments
>      minor revision to unit test.
>      Note: the unit test is intentionally the same as other locking tests.
> 
>  app/test/meson.build                        |   2 +
>  app/test/test_pflock.c                      | 197 +++++++++++++++++++
>  lib/librte_eal/arm/include/meson.build      |   1 +
>  lib/librte_eal/arm/include/rte_pflock.h     |  18 ++
>  lib/librte_eal/include/generic/rte_pflock.h | 205 ++++++++++++++++++++
>  lib/librte_eal/ppc/include/meson.build      |   1 +
>  lib/librte_eal/ppc/include/rte_pflock.h     |  17 ++
>  lib/librte_eal/x86/include/meson.build      |   1 +
>  lib/librte_eal/x86/include/rte_pflock.h     |  18 ++
>  9 files changed, 460 insertions(+)
>  create mode 100644 app/test/test_pflock.c  create mode 100644
> lib/librte_eal/arm/include/rte_pflock.h
>  create mode 100644 lib/librte_eal/include/generic/rte_pflock.h
>  create mode 100644 lib/librte_eal/ppc/include/rte_pflock.h
>  create mode 100644 lib/librte_eal/x86/include/rte_pflock.h
> 

<snip>

> diff --git a/app/test/test_pflock.c b/app/test/test_pflock.c new file mode
> 100644 index 000000000000..6922bbc2f813
> --- /dev/null
> +++ b/app/test/test_pflock.c
> @@ -0,0 +1,197 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2021 Microsoft Corporation  */
> +
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <inttypes.h>
> +#include <unistd.h>
> +#include <sys/queue.h>
> +#include <string.h>
> +
> +#include <rte_common.h>
> +#include <rte_memory.h>
> +#include <rte_per_lcore.h>
> +#include <rte_launch.h>
> +#include <rte_pause.h>
> +#include <rte_pflock.h>
> +#include <rte_eal.h>
> +#include <rte_lcore.h>
> +#include <rte_cycles.h>
> +
> +#include "test.h"
> +

<snip>

> +
> +/*
> + * - There is a global pflock and a table of pflocks (one per lcore).
> + *
> + * - The test function takes all of these locks and launches the
> + *   ``test_pflock_per_core()`` function on each core (except the main).
> + *
> + *   - The function takes the global write lock, display something,
> + *     then releases the global lock.
> + *   - Then, it takes the per-lcore write lock, display something, and
> + *     releases the per-core lock.
> + *   - Finally, a read lock is taken during 100 ms, then released.
> + *
> + * - The main function unlocks the per-lcore locks sequentially and
> + *   waits between each lock. This triggers the display of a message
> + *   for each core, in the correct order.
> + *
> + *   Then, it tries to take the global write lock and display the last
> + *   message. The autotest script checks that the message order is correct.
How does the autotest script does this?

> + */
> +static int
> +test_pflock(void)
> +{
> +	int i;
> +
> +	rte_pflock_init(&sl);
> +	for (i = 0; i < RTE_MAX_LCORE; i++)
> +		rte_pflock_init(&sl_tab[i]);
> +
> +	rte_pflock_write_lock(&sl);
> +
> +	RTE_LCORE_FOREACH_WORKER(i) {
> +		rte_pflock_write_lock(&sl_tab[i]);
> +		rte_eal_remote_launch(test_pflock_per_core, NULL, i);
> +	}
> +
> +	rte_pflock_write_unlock(&sl);
> +
> +	RTE_LCORE_FOREACH_WORKER(i) {
> +		rte_pflock_write_unlock(&sl_tab[i]);
> +		rte_delay_ms(100);
> +	}
> +
> +	rte_pflock_write_lock(&sl);
> +	/* this message should be the last message of test */
> +	printf("Global write lock taken on main core %u\n", rte_lcore_id());
> +	rte_pflock_write_unlock(&sl);
> +
> +	rte_eal_mp_wait_lcore();
> +
> +	if (test_pflock_perf() < 0)
> +		return -1;
> +
> +	return 0;
> +}
> +
> +REGISTER_TEST_COMMAND(pflock_autotest, test_pflock);

<snip>