From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: "Van Haaren, Harry" <harry.van.haaren@intel.com>,
Phil Yang <Phil.Yang@arm.com>, "dev@dpdk.org" <dev@dpdk.org>
Cc: "thomas@monjalon.net" <thomas@monjalon.net>,
"david.marchand@redhat.com" <david.marchand@redhat.com>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
"jerinj@marvell.com" <jerinj@marvell.com>,
"hemant.agrawal@nxp.com" <hemant.agrawal@nxp.com>,
Gavin Hu <Gavin.Hu@arm.com>, nd <nd@arm.com>,
"stable@dpdk.org" <stable@dpdk.org>,
"Eads, Gage" <gage.eads@intel.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
nd <nd@arm.com>
Subject: Re: [dpdk-stable] [PATCH v2 1/6] service: fix race condition for MT unsafe service
Date: Wed, 29 Apr 2020 22:48:59 +0000 [thread overview]
Message-ID: <DBBPR08MB4646F542ABAC37DB1FE8166598AD0@DBBPR08MB4646.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <BYAPR11MB314336FF974684E6568EA203D7AD0@BYAPR11MB3143.namprd11.prod.outlook.com>
Hi Harry,
Thanks for getting back on this.
<snip>
> > Subject: [PATCH v2 1/6] service: fix race condition for MT unsafe
> > service
> >
> > From: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> >
> > The 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>
> > ---
>
> Thanks for spinning a new revision - based on ML discussion previously, it
> seems like the "use service-run-count" to avoid this race would be a complex
> solution.
>
> Suggesting the following;
> 1) Take the approach as per this patch, to always take the atomic, fixing the
> race condition.
Ok
> 2) Add an API to service-cores, which allows "committing" of mappings.
> Committing the mapping would imply that the mappings will not be changed
> in future. With runtime-remapping being removed from the equation, the
> existing branch-over-atomic optimization is valid again.
Ok. Just to make sure I understand this:
a) on the data plane, if commit API is called (probably a new state variable) and num_mapped_cores is set to 1, there is no need to take the lock.
b) possible implementation of the commit API would check if num_mapped_cores for the service is set to 1 and set a variable to indicate that the lock is not required.
What do you think about asking the application to set the service capability to MT_SAFE if it knows that the service will run on a single core? This would require us to change the documentation and does not require additional code.
>
> So this would offer applications two situations
> A) No application change: possible performance regression due to atomic
> always taken.
> B) Call "commit" API, and regain the performance as per previous DPDK
> versions.
>
> Thoughts/opinions on the above? I've flagged the rest of the patchset for
> review ASAP. Regards, -Harry
>
> > 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 70d17a5..b8c465e 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:[~2020-04-29 22:49 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 [this message]
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
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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