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From: Matan Azrad <matan@mellanox.com>
To: "Benoit Ganne (bganne)" <bganne@cisco.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] net/mlx5: fix link state update
Date: Mon, 30 Mar 2020 13:44:01 +0000
Message-ID: <AM0PR0502MB4019731AACBC90CB7744D5B4D2CB0@AM0PR0502MB4019.eurprd05.prod.outlook.com> (raw)
In-Reply-To: <CH2PR11MB4327BBBE24E9B7AF788ABE36C1CB0@CH2PR11MB4327.namprd11.prod.outlook.com>


Hi
 From: Benoit Ganne 
> Sent: Monday, March 30, 2020 3:03 PM
> To: Matan Azrad <matan@mellanox.com>; dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] net/mlx5: fix link state update
> 
> Hi Matan,
> 
> >>>> mlx5 PMD refuses to update link state if link speed is defined but
> >>>> status is down or if link speed is undefined but status is up, even
> >>>> if the ioctl() succeeded.
> >>>> This prevents application to detect link up/down event, especially
> >>>> when the link speed is not correctly detected.
> >>> Do you use the wait option? Or no wait?
> >> We are using the no wait option.
> > I suggest to call again if failed for N retries time.
> 
> Unfortunately it will not solve our problem: if link speed is undefined but the
> link is up then the test '!dev_link.link_speed && dev_link.link_status' at
> https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgit.dp
> dk.org%2Fdpdk%2Ftree%2Fdrivers%2Fnet%2Fmlx5%2Fmlx5_ethdev.c%23n8
> 99&amp;data=02%7C01%7Cmatan%40mellanox.com%7C8a0fb9f9ba94422a4a
> 4208d7d4a2539c%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%7C0%7C637
> 211665962283891&amp;sdata=%2FExOJyhm0Bi4kkp434P0U4kRpQs7U0knuTa
> kvsWFO5Q%3D&amp;reserved=0 will always be true and the function will
> always return EAGAIN.
> This actually happens in Azure with CX4-Lx VFs.
> 
> >> What I meant was to let the app decide whether it should retry or
> >> not, based on the data it gets.
> >> Right now, the PMD *prevents* the app to get link state if the link
> >> speed is undefined even if the app does not care about link speed.
> 
> > In mlx5 this is not the case, we have no one updated and second not -
> > there are going together:
> > You can see that we have 2 different system calls: 1 to get up\down
> > and second to get link speed.
> > If link speed doesn't appropriate to the link state it may say that
> > something was changed between the calls and the link status we got
> > from the first call is not correct anymore.
> > In this case, we should call both calls again, that’s what we are
> > doing in "nowait" option.
> > If the user doesn't want "nowait" option, (means PMD is not allowed to
> > take more time for response) he should call again when the callback
> > failed in the time and retries manner the user prefers.
> 
> Ok, now I understand the logic behind the current behavior: the 2 syscalls
> being not atomics, you try to detect inconsistencies that way.
> But if the link speed is undefined, then the state will never be correctly
> updated.

Why link speed is undefined?
Old kernel?
Kernel mlx5 driver issue?

Do you know?

> I still believe it is unnecessarily heavy-handed: in most networking application
> I have seen (and I have 2 examples of current shipping networking products),
> a missing link speed is not critical whereas link being reported as down means
> no traffic flowing.
> 
> Best
> ben

  reply	other threads:[~2020-03-30 13:44 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-27 17:24 Benoît Ganne
2020-03-29  7:00 ` Matan Azrad
2020-03-30  9:55   ` Benoit Ganne (bganne)
2020-03-30 10:12     ` Matan Azrad
2020-03-30 12:03       ` Benoit Ganne (bganne)
2020-03-30 13:44         ` Matan Azrad [this message]
2020-03-30 13:53           ` Benoit Ganne (bganne)
2020-03-30 16:13             ` Matan Azrad
2020-04-01 10:17               ` Benoit Ganne (bganne)
2020-04-01 12:46                 ` Matan Azrad
2020-04-07 12:54               ` Thomas Monjalon
2020-04-07 13:41                 ` Benoit Ganne (bganne)
2020-11-19  8:30                   ` Matan Azrad
2020-11-19 14:20 ` [dpdk-dev] [PATCH v2] " Raslan Darawsheh
2020-11-19 16:27   ` Raslan Darawsheh
2020-11-19 17:48   ` Ferruh Yigit
2020-11-19 18:42     ` Thomas Monjalon
2020-11-20 10:51       ` Ferruh Yigit
2020-11-20 13:50         ` Thomas Monjalon
2020-11-20 14:21           ` Ferruh Yigit
2020-11-22 10:03             ` Raslan Darawsheh
2020-11-22 10:04   ` [dpdk-dev] [PATCH v3] net/mlx5: allow unknown link speed Raslan Darawsheh
2020-11-22 12:58     ` Raslan Darawsheh

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