From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: Harry van Haaren <harry.van.haaren@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>
Cc: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
"Morten Brørup" <mb@smartsharesystems.com>, nd <nd@arm.com>,
nd <nd@arm.com>
Subject: RE: [PATCH 2/2] service: fix potential stats race-condition on MT services
Date: Fri, 8 Jul 2022 15:16:18 +0000 [thread overview]
Message-ID: <DBAPR08MB58145179979AD3BDA401FE4798829@DBAPR08MB5814.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20220708125645.3141464-2-harry.van.haaren@intel.com>
<snip>
>
> This commit fixes a potential racey-add that could occur if multiple service-
> lcores were executing the same MT-safe service at the same time, with
> service statistics collection enabled.
>
> Because multiple threads can run and execute the service, the stats values
> can have multiple writer threads, resulting in the requirement of using
> atomic addition for correctness.
>
> Note that when a MT unsafe service is executed, a spinlock is held, so the
> stats increments are protected. This fact is used to avoid executing atomic
> add instructions when not required.
>
> This patch causes a 1.25x increase in cycle-cost for polling a MT safe service
> when statistics are enabled. No change was seen for MT unsafe services, or
> when statistics are disabled.
>
> Reported-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> Suggested-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Suggested-by: Morten Brørup <mb@smartsharesystems.com>
> Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
>
> ---
> ---
> lib/eal/common/rte_service.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/lib/eal/common/rte_service.c b/lib/eal/common/rte_service.c
> index ef31b1f63c..f045e74ef3 100644
> --- a/lib/eal/common/rte_service.c
> +++ b/lib/eal/common/rte_service.c
> @@ -363,9 +363,15 @@ service_runner_do_callback(struct
> rte_service_spec_impl *s,
> uint64_t start = rte_rdtsc();
> s->spec.callback(userdata);
> uint64_t end = rte_rdtsc();
> - s->cycles_spent += end - start;
> + uint64_t cycles = end - start;
> cs->calls_per_service[service_idx]++;
> - s->calls++;
> + if (service_mt_safe(s)) {
> + __atomic_fetch_add(&s->cycles_spent, cycles,
> __ATOMIC_RELAXED);
> + __atomic_fetch_add(&s->calls, 1,
> __ATOMIC_RELAXED);
> + } else {
> + s->cycles_spent += cycles;
> + s->calls++;
This is still a problem from a reader perspective. It is possible that the writes could be split while a reader is reading the stats. These need to be atomic adds.
> + }
> } else
> s->spec.callback(userdata);
> }
> --
> 2.32.0
next prev parent reply other threads:[~2022-07-08 15:16 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-08 12:56 [PATCH 1/2] test/service: add perf measurements for with stats mode Harry van Haaren
2022-07-08 12:56 ` [PATCH 2/2] service: fix potential stats race-condition on MT services Harry van Haaren
2022-07-08 13:23 ` Morten Brørup
2022-07-08 13:44 ` Van Haaren, Harry
2022-07-08 14:14 ` Morten Brørup
2022-07-08 13:48 ` Mattias Rönnblom
2022-07-08 15:16 ` Honnappa Nagarahalli [this message]
2022-07-08 15:31 ` Van Haaren, Harry
2022-07-08 16:21 ` Bruce Richardson
2022-07-08 16:33 ` Honnappa Nagarahalli
2022-07-08 20:02 ` Mattias Rönnblom
2022-07-08 16:29 ` Morten Brørup
2022-07-08 16:45 ` Honnappa Nagarahalli
2022-07-08 17:22 ` Morten Brørup
2022-07-08 17:39 ` Honnappa Nagarahalli
2022-07-08 18:08 ` Morten Brørup
2022-09-06 16:13 ` [PATCH 1/6] service: reduce statistics overhead for parallel services Mattias Rönnblom
2022-09-06 16:13 ` [PATCH 2/6] service: introduce per-lcore cycles counter Mattias Rönnblom
2022-09-06 16:13 ` [PATCH 3/6] service: reduce average case service core overhead Mattias Rönnblom
2022-10-03 13:33 ` Van Haaren, Harry
2022-10-03 14:32 ` Mattias Rönnblom
2022-09-06 16:13 ` [PATCH 4/6] service: tweak cycle statistics semantics Mattias Rönnblom
2022-09-07 8:41 ` Morten Brørup
2022-10-03 13:45 ` Van Haaren, Harry
2022-09-06 16:13 ` [PATCH 5/6] event/sw: report idle when no work is performed Mattias Rönnblom
2022-09-06 16:13 ` [PATCH 6/6] service: provide links to functions in documentation Mattias Rönnblom
2022-10-03 8:06 ` [PATCH 1/6] service: reduce statistics overhead for parallel services David Marchand
2022-10-03 8:40 ` Mattias Rönnblom
2022-10-03 9:53 ` David Marchand
2022-10-03 11:37 ` Mattias Rönnblom
2022-10-03 13:03 ` Van Haaren, Harry
2022-10-03 13:33 ` Van Haaren, Harry
2022-10-03 14:37 ` Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 0/6] Service cores performance and statistics improvements Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 1/6] service: reduce statistics overhead for parallel services Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 2/6] service: introduce per-lcore cycles counter Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 3/6] service: reduce average case service core overhead Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 4/6] service: tweak cycle statistics semantics Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 5/6] event/sw: report idle when no work is performed Mattias Rönnblom
2022-10-05 9:16 ` [PATCH v2 6/6] service: provide links to functions in documentation Mattias Rönnblom
2022-10-05 9:49 ` [PATCH v2 0/6] Service cores performance and statistics improvements Morten Brørup
2022-10-05 10:14 ` Mattias Rönnblom
2022-10-05 13:39 ` David Marchand
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