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From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
To: 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>,
	"Honnappa.Nagarahalli@arm.com" <Honnappa.Nagarahalli@arm.com>,
	"gavin.hu@arm.com" <gavin.hu@arm.com>, "nd@arm.com" <nd@arm.com>,
	"Honnappa Nagarahalli" <honnappa.nagarahalli@arm.com>,
	"stable@dpdk.org" <stable@dpdk.org>,
	"Eads, Gage" <gage.eads@intel.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>
Subject: Re: [dpdk-stable] [PATCH v2 1/6] service: fix race condition for MT unsafe service
Date: Wed, 29 Apr 2020 16:51:39 +0000	[thread overview]
Message-ID: <BYAPR11MB314336FF974684E6568EA203D7AD0@BYAPR11MB3143.namprd11.prod.outlook.com> (raw)
In-Reply-To: <1587659482-27133-2-git-send-email-phil.yang@arm.com>

> -----Original Message-----
> From: Phil Yang <phil.yang@arm.com>
> Sent: Thursday, April 23, 2020 5:31 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>; dev@dpdk.org
> Cc: thomas@monjalon.net; david.marchand@redhat.com; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; jerinj@marvell.com;
> hemant.agrawal@nxp.com; Honnappa.Nagarahalli@arm.com;
> gavin.hu@arm.com; nd@arm.com; Honnappa Nagarahalli
> <honnappa.nagarahalli@arm.com>; stable@dpdk.org
> 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.
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.

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


  reply	other threads:[~2020-04-29 16:51 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 [this message]
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
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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