From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
To: Phil Yang <phil.yang@arm.com>,
"thomas@monjalon.net" <thomas@monjalon.net>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
"stephen@networkplumber.org" <stephen@networkplumber.org>,
"maxime.coquelin@redhat.com" <maxime.coquelin@redhat.com>,
"dev@dpdk.org" <dev@dpdk.org>
Cc: "david.marchand@redhat.com" <david.marchand@redhat.com>,
"jerinj@marvell.com" <jerinj@marvell.com>,
"hemant.agrawal@nxp.com" <hemant.agrawal@nxp.com>,
"Honnappa.Nagarahalli@arm.com" <Honnappa.Nagarahalli@arm.com>,
"gavin.hu@arm.com" <gavin.hu@arm.com>,
"ruifeng.wang@arm.com" <ruifeng.wang@arm.com>,
"joyce.kong@arm.com" <joyce.kong@arm.com>,
"nd@arm.com" <nd@arm.com>,
Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>,
"stable@dpdk.org" <stable@dpdk.org>
Subject: Re: [dpdk-stable] [PATCH v3 09/12] service: avoid race condition for MT unsafe service
Date: Fri, 3 Apr 2020 11:58:08 +0000 [thread overview]
Message-ID: <BYAPR11MB3143B499A98B511E39EC6F5AD7C70@BYAPR11MB3143.namprd11.prod.outlook.com> (raw)
In-Reply-To: <1584407863-774-10-git-send-email-phil.yang@arm.com>
> From: Phil Yang <phil.yang@arm.com>
> Sent: Tuesday, March 17, 2020 1:18 AM
> To: thomas@monjalon.net; Van Haaren, Harry <harry.van.haaren@intel.com>;
> Ananyev, Konstantin <konstantin.ananyev@intel.com>;
> stephen@networkplumber.org; maxime.coquelin@redhat.com; dev@dpdk.org
> Cc: david.marchand@redhat.com; jerinj@marvell.com; hemant.agrawal@nxp.com;
> Honnappa.Nagarahalli@arm.com; gavin.hu@arm.com; ruifeng.wang@arm.com;
> joyce.kong@arm.com; nd@arm.com; Honnappa Nagarahalli
> <honnappa.nagarahalli@arm.com>; stable@dpdk.org
> Subject: [PATCH v3 09/12] service: avoid race condition for MT unsafe service
>
> From: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
>
> There has possible that a MT unsafe service might get configured to
> run on another core while the service is running currently. This
> might result in the MT unsafe service running on multiple cores
> simultaneously. Use 'execute_lock' always when the service is
> MT unsafe.
>
> Fixes: e9139a32f6e8 ("service: add function to run on app lcore")
> Cc: stable@dpdk.org
>
> Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Phil Yang <phil.yang@arm.com>
> Reviewed-by: Gavin Hu <gavin.hu@arm.com>
We should put "fix" in the title, once converged on an implementation.
Regarding Fixes and stable backport, we should consider if
fixing this in stable with a performance degradation, fixing with more
complex solution, or documenting a known issue a better solution.
This fix (always taking the atomic lock) will have a negative performance
impact on existing code using services. We should investigate a way
to fix it without causing datapath performance degradation.
I think there is a way to achieve this by moving more checks/time
to the control path (lcore updating the map), and not forcing the
datapath lcore to always take an atomic.
In this particular case, we have a counter for number of iterations
that a service has done. If this increments we know that the lcore
running the service has re-entered the critical section, so would
see an updated "needs atomic" flag.
This approach may introduce a predictable branch on the datapath,
however the cost of a predictable branch vs always taking an atomic
is order(s?) of magnitude, so a branch is much preferred.
It must be possible to avoid the datapath overhead using a scheme
like this. It will likely be more complex than your proposed change
below, however if it avoids datapath performance drops I feel that
a more complex solution is worth investigating at least.
A unit test is required to validate a fix like this - although perhaps
found by inspection/review, a real-world test to validate would give
confidence.
Thoughts on such an approach?
> ---
> lib/librte_eal/common/rte_service.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/lib/librte_eal/common/rte_service.c
> b/lib/librte_eal/common/rte_service.c
> index 557b5a9..32a2f8a 100644
> --- a/lib/librte_eal/common/rte_service.c
> +++ b/lib/librte_eal/common/rte_service.c
> @@ -50,6 +50,10 @@ struct rte_service_spec_impl {
> uint8_t internal_flags;
>
> /* per service statistics */
> + /* Indicates how many cores the service is mapped to run on.
> + * It does not indicate the number of cores the service is running
> + * on currently.
> + */
> rte_atomic32_t num_mapped_cores;
> uint64_t calls;
> uint64_t cycles_spent;
> @@ -370,12 +374,7 @@ service_run(uint32_t i, struct core_state *cs, uint64_t
> service_mask,
>
> cs->service_active_on_lcore[i] = 1;
>
> - /* check do we need cmpset, if MT safe or <= 1 core
> - * mapped, atomic ops are not required.
> - */
> - const int use_atomics = (service_mt_safe(s) == 0) &&
> - (rte_atomic32_read(&s->num_mapped_cores) > 1);
> - if (use_atomics) {
> + if (service_mt_safe(s) == 0) {
> if (!rte_atomic32_cmpset((uint32_t *)&s->execute_lock, 0, 1))
> return -EBUSY;
>
> --
> 2.7.4
next prev parent reply other threads:[~2020-04-03 11:58 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1583862551-2049-1-git-send-email-phil.yang@arm.com>
2020-03-10 17:49 ` [dpdk-stable] [PATCH 05/10] service: remove rte prefix from static functions Phil Yang
2020-03-10 17:49 ` [dpdk-stable] [PATCH 06/10] service: remove redundant code Phil Yang
2020-03-10 17:49 ` [dpdk-stable] [PATCH 07/10] service: avoid race condition for MT unsafe service Phil Yang
2020-03-10 17:49 ` [dpdk-stable] [PATCH 08/10] service: identify service running on another core correctly Phil Yang
[not found] ` <1583993624-20446-1-git-send-email-phil.yang@arm.com>
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 05/10] service: remove rte prefix from static functions Phil Yang
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 06/10] service: remove redundant code Phil Yang
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 07/10] service: avoid race condition for MT unsafe service Phil Yang
2020-03-12 6:13 ` [dpdk-stable] [PATCH v2 08/10] service: identify service running on another core correctly Phil Yang
[not found] ` <1583999071-22872-1-git-send-email-phil.yang@arm.com>
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 05/10] service: remove rte prefix from static functions Phil Yang
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 06/10] service: remove redundant code Phil Yang
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 07/10] service: avoid race condition for MT unsafe service Phil Yang
2020-03-12 7:44 ` [dpdk-stable] [PATCH v2 08/10] service: identify service running on another core correctly Phil Yang
[not found] ` <1584407863-774-1-git-send-email-phil.yang@arm.com>
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 07/12] service: remove rte prefix from static functions Phil Yang
2020-04-03 11:57 ` Van Haaren, Harry
2020-04-08 10:14 ` Phil Yang
2020-04-08 10:36 ` Van Haaren, Harry
2020-04-08 10:49 ` Phil Yang
2020-04-05 21:35 ` Honnappa Nagarahalli
2020-04-08 10:14 ` Phil Yang
[not found] ` <1587659482-27133-1-git-send-email-phil.yang@arm.com>
2020-04-23 16:31 ` [dpdk-stable] [PATCH v2 1/6] service: fix race condition for MT unsafe service Phil Yang
2020-04-29 16:51 ` Van Haaren, Harry
2020-04-29 22:48 ` Honnappa Nagarahalli
2020-05-01 14:21 ` Van Haaren, Harry
2020-05-01 14:56 ` Honnappa Nagarahalli
2020-05-01 17:51 ` Van Haaren, Harry
2020-04-23 16:31 ` [dpdk-stable] [PATCH v2 2/6] service: identify service running on another core correctly Phil Yang
[not found] ` <20200502000245.11071-1-honnappa.nagarahalli@arm.com>
2020-05-02 0:02 ` [dpdk-stable] [PATCH v3 1/6] service: fix race condition for MT unsafe service Honnappa Nagarahalli
2020-05-05 14:48 ` Van Haaren, Harry
2020-05-02 0:02 ` [dpdk-stable] [PATCH v3 2/6] service: identify service running on another core correctly Honnappa Nagarahalli
2020-05-05 14:48 ` Van Haaren, Harry
[not found] ` <20200505211732.25291-1-honnappa.nagarahalli@arm.com>
2020-05-05 21:17 ` [dpdk-stable] [PATCH v4 1/6] service: fix race condition for MT unsafe service Honnappa Nagarahalli
2020-05-05 21:17 ` [dpdk-stable] [PATCH v4 2/6] service: fix identification of service running on other lcore Honnappa Nagarahalli
[not found] ` <1588760683-11027-1-git-send-email-phil.yang@arm.com>
2020-05-06 10:24 ` [dpdk-stable] [PATCH v5 1/6] service: fix race condition for MT unsafe service Phil Yang
2020-05-06 10:24 ` [dpdk-stable] [PATCH v5 2/6] service: fix identification of service running on other lcore Phil Yang
[not found] ` <1588778884-13047-1-git-send-email-phil.yang@arm.com>
2020-05-06 15:27 ` [dpdk-stable] [PATCH v6 1/6] service: fix race condition for MT unsafe service Phil Yang
2020-05-06 15:28 ` [dpdk-stable] [PATCH v6 2/6] service: fix identification of service running on other lcore Phil Yang
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 08/12] service: remove redundant code Phil Yang
2020-04-03 11:58 ` Van Haaren, Harry
2020-04-05 18:35 ` Honnappa Nagarahalli
2020-04-08 10:15 ` Phil Yang
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 09/12] service: avoid race condition for MT unsafe service Phil Yang
2020-04-03 11:58 ` Van Haaren, Harry [this message]
2020-04-04 18:03 ` Honnappa Nagarahalli
2020-04-08 18:05 ` Van Haaren, Harry
2020-04-09 1:31 ` Honnappa Nagarahalli
2020-04-09 16:46 ` Van Haaren, Harry
2020-04-18 6:21 ` Honnappa Nagarahalli
2020-04-21 17:43 ` Van Haaren, Harry
2020-03-17 1:17 ` [dpdk-stable] [PATCH v3 10/12] service: identify service running on another core correctly Phil Yang
2020-04-03 11:58 ` Van Haaren, Harry
2020-04-05 2:43 ` Honnappa Nagarahalli
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