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From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	David Marchand <david.marchand@redhat.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"igor.romanov@oktetlabs.ru" <igor.romanov@oktetlabs.ru>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>, nd <nd@arm.com>,
	"aconole@redhat.com" <aconole@redhat.com>,
	"l.wojciechow@partner.samsung.com"
	<l.wojciechow@partner.samsung.com>,
	"Phil Yang" <Phil.Yang@arm.com>,
	"Eads, Gage" <gage.eads@intel.com>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v2 1/2] service: add API to retrieve service core active
Date: Thu, 23 Jul 2020 16:59:03 +0000	[thread overview]
Message-ID: <BYAPR11MB3143B266E153E23ED9CC0994D7760@BYAPR11MB3143.namprd11.prod.outlook.com> (raw)
In-Reply-To: <DB6PR0802MB2216F888CD92DD1F55357A8998790@DB6PR0802MB2216.eurprd08.prod.outlook.com>

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Wednesday, July 22, 2020 7:50 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>; David Marchand
> <david.marchand@redhat.com>
> Cc: dev@dpdk.org; igor.romanov@oktetlabs.ru; Yigit, Ferruh
> <ferruh.yigit@intel.com>; nd <nd@arm.com>; aconole@redhat.com;
> l.wojciechow@partner.samsung.com; Phil Yang <Phil.Yang@arm.com>;
> Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Eads, Gage
> <gage.eads@intel.com>; nd <nd@arm.com>
> Subject: RE: [PATCH v2 1/2] service: add API to retrieve service core active
> 
> + Gage (as I referring to his commit below)
> 
> <snip>
> 
> >
> > > > > > +/**
> > > > > > + * Reports if a service lcore is currently running.
> > > > > > + * @retval 0 Service thread is not active, and has been returned to
> > EAL.
> > > > > > + * @retval 1 Service thread is in the service core polling loop.
> > > > > > + * @retval -EINVAL Invalid *lcore_id* provided.
> > > > > > + */
> > > > > > +__rte_experimental
> > > > > > +int32_t rte_service_lcore_active(uint32_t lcore_id);
> > > > > Would 'rte_service_lcore_may_be_active' better? It would be inline
> > > > > with
> > > > 'rte_service_may_be_active'?
> >
> > I think the implementation behind the API is different, so I think _may_be_ is
> > not appropriate for service_lcore_active, keeping same function name for v3.
> >
> > rte_service_lcore_active() checks at a particular point in the calling thread if
> > another thread is active *at that time*. It is either active or not. This is
> > defined, it is deterministic in that the result is either yes or no, and there is
> > no ambiguity at any given check. You're right the value can change *just* after
> > the check - but at the time of the check the answer was deterministic.
> >
> > rte_service_may_be_active() checks if a service *could* be run by a service
> > core. It is not deterministic. A service lcore only sets a service as "active on
> > lcore" (or not active) when it polls it - this opens a window of
> > nondeterministic result. When a runstate is set to off, there is a window of
> > "unknown" before we know certainly that the service is not run on a service
> > core anymore. That is why I believe the _may_be_ is appropriate for this API,
> > it shows this non determinism.
> >
> 
> I am looking at this from the application usage perspective (not the
> implementation). I am pointing to the similarity that exists with the new API. i.e.
> when 'rte_service_lcore_stop' is called, it is not known if the service lcore has
> stopped. If 'rte_service_lcore_active' returns 1, it indicates the lcore 'may be'
> active (the reasoning could be different in this case), it is not guaranteed that it
> is active by the time caller checks it. But when the API returns 0, it guarantees
> that the service lcore (assuming it was started and verified that it was started),
> has stopped.
> 
> Looking at the commit e30dd31847d212cd1b766612cbd980c7d8240baa that
> added the 'rte_service_may_be_active', the use case is a mechanism to identify a
> quiescent state after a service was stopped.
> The use case for the new API is also the same. We want to identify a quiescent
> state after a service lcore is stopped.
> 
> <snip>

Sure - if you feel strongly that we need the _may_be_ to focus the end-users
attention that this is a cross-thread check and has some quiescent property, lets
add it to err on the side of obvious. Will change API name for v3.

Saw the other feedback on patches too - will incorporate and send ASAP, might need
till tomorrow to get it done.

  reply	other threads:[~2020-07-23 16:59 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200720120850eucas1p10debcafa273d244a7e63d225c50cc9df@eucas1p1.samsung.com>
2020-07-20 12:09 ` [dpdk-dev] [PATCH] service: fix stop API to wait for service thread Harry van Haaren
2020-07-20 12:51   ` Lukasz Wojciechowski
2020-07-20 14:20     ` Van Haaren, Harry
2020-07-20 14:38   ` [dpdk-dev] [PATCH v2 1/2] service: add API to retrieve service core active Harry van Haaren
2020-07-20 14:38     ` [dpdk-dev] [PATCH v2 2/2] test/service: fix race condition on stopping lcore Harry van Haaren
2020-07-20 17:45       ` Lukasz Wojciechowski
2020-07-21  8:38       ` Phil Yang
2020-07-22 10:26         ` Van Haaren, Harry
2020-07-20 17:45     ` [dpdk-dev] [PATCH v2 1/2] service: add API to retrieve service core active Lukasz Wojciechowski
2020-07-21  7:47     ` Phil Yang
2020-07-21 19:43     ` Honnappa Nagarahalli
2020-07-21 19:50       ` David Marchand
2020-07-21 20:23         ` Honnappa Nagarahalli
2020-07-22 10:14           ` Van Haaren, Harry
2020-07-22 18:50             ` Honnappa Nagarahalli
2020-07-23 16:59               ` Van Haaren, Harry [this message]
2020-07-22 10:37     ` [dpdk-dev] [PATCH v3 " Harry van Haaren
2020-07-22 10:37       ` [dpdk-dev] [PATCH v3 2/2] test/service: fix race condition on stopping lcore Harry van Haaren
2020-07-22 21:40         ` Honnappa Nagarahalli
2020-07-22 21:39       ` [dpdk-dev] [PATCH v3 1/2] service: add API to retrieve service core active Honnappa Nagarahalli
2020-07-24 12:45       ` [dpdk-dev] [PATCH v4 " Harry van Haaren
2020-07-24 12:45         ` [dpdk-dev] [PATCH v4 2/2] test/service: fix race condition on stopping lcore Harry van Haaren
2020-07-24 13:45         ` [dpdk-dev] [PATCH v5 1/2] service: add API to retrieve service core active Harry van Haaren
2020-07-24 13:45           ` [dpdk-dev] [PATCH v5 2/2] test/service: fix race condition on stopping lcore Harry van Haaren
2020-09-14  8:36             ` David Marchand
2020-09-14 14:33               ` Van Haaren, Harry
2020-09-14 14:31           ` [dpdk-dev] [PATCH v6 1/2] service: add API to retrieve service core active Harry van Haaren
2020-09-14 14:31             ` [dpdk-dev] [PATCH v6 2/2] test/service: fix race condition on stopping lcore Harry van Haaren
2020-09-21 14:51               ` David Marchand
2020-10-13 19:45                 ` David Marchand
2020-10-15  8:11                   ` Van Haaren, Harry

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