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From: "Benoit Ganne (bganne)" <bganne@cisco.com>
To: Matan Azrad <matan@mellanox.com>, "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] net/mlx5: fix link state update
Date: Mon, 30 Mar 2020 12:03:10 +0000
Message-ID: <CH2PR11MB4327BBBE24E9B7AF788ABE36C1CB0@CH2PR11MB4327.namprd11.prod.outlook.com> (raw)
In-Reply-To: <AM0PR0502MB4019095F23AC15AEEEC2088DD2CB0@AM0PR0502MB4019.eurprd05.prod.outlook.com>

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 http://git.dpdk.org/dpdk/tree/drivers/net/mlx5/mlx5_ethdev.c#n899 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.
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.


  reply	other threads:[~2020-03-30 12:03 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) [this message]
2020-03-30 13:44         ` Matan Azrad
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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