netdev - Re: [PATCH net-next] net: core: devlink: add new trap action HARD

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Message-ID: <20210122171223.1f7b55b7@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 22 Jan 2021 17:12:23 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Oleksandr Mazur <oleksandr.mazur@...ision.eu>
Cc:     Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jiri@...dia.com" <jiri@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: core: devlink: add new trap action
 HARD_DROP

On Fri, 22 Jan 2021 08:36:01 +0000 Oleksandr Mazur wrote:
> On Thu, 21 Jan 2021 14:21:52 +0200 Ido Schimmel wrote:
> > On Thu, Jan 21, 2021 at 01:29:37PM +0200, Oleksandr Mazur wrote:  
> > > Add new trap action HARD_DROP, which can be used by the
> > > drivers to register traps, where it's impossible to get
> > > packet reported to the devlink subsystem by the device
> > > driver, because it's impossible to retrieve dropped packet
> > > from the device itself.
> > > In order to use this action, driver must also register
> > > additional devlink operation - callback that is used
> > > to retrieve number of packets that have been dropped by
> > > the device.    
> > 
> > Are these global statistics about number of packets the hardware dropped
> > for a specific reason or are these per-port statistics?
> > 
> > It's a creative use of devlink-trap interface, but I think it makes
> > sense. Better to re-use an existing interface than creating yet another
> > one.  
> 
> > Not sure if I agree, if we can't trap why is it a trap?
> > It's just a counter.  
> 
> It's just another ACTION for trap item. Action however can be
> switched, e.g. from HARD_DROP to MIRROR.
> 
> The thing is to be able to configure specific trap to be dropped, and
> provide a way for the device to report back how many packets have
> been dropped. If device is able to report the packet itself, then
> devlink would be in charge of counting. If not, there should be a way
> to retrieve these statistics from the devlink.

Sure, but the action is drop. The statistics on the trap are orthogonal
to the action.