netdev - Re: [PATCH net-next v2] net: sched: implement action-specific terse dump

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Message-ID: <20201105085115.609cade1@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 5 Nov 2020 08:51:15 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Vlad Buslov <vlad@...lov.dev>, netdev@...r.kernel.org,
        davem@...emloft.net, xiyou.wangcong@...il.com, jiri@...nulli.us
Subject: Re: [PATCH net-next v2] net: sched: implement action-specific terse
 dump

On Thu, 5 Nov 2020 06:48:48 -0500 Jamal Hadi Salim wrote:
> On 2020-11-04 7:39 p.m., Jakub Kicinski wrote:
> > On Mon,  2 Nov 2020 22:12:43 +0200 Vlad Buslov wrote:  
> >> Allow user to request action terse dump with new flag value
> >> TCA_FLAG_TERSE_DUMP. Only output essential action info in terse dump (kind,
> >> stats, index and cookie, if set by the user when creating the action). This
> >> is different from filter terse dump where index is excluded (filter can be
> >> identified by its own handle).
> >>
> >> Move tcf_action_dump_terse() function to the beginning of source file in
> >> order to call it from tcf_dump_walker().
> >>
> >> Signed-off-by: Vlad Buslov <vlad@...lov.dev>
> >> Suggested-by: Jamal Hadi Salim <jhs@...atatu.com>  
> > 
> > Jiri, Cong, can I get an ack?
> > 
> > The previous terse dump made sense because it fulfilled the need of
> > an important user (OvS).   
> 
> The requirement is to save on how much data crosses between user
> space and the kernel. If you are polling the kernel every second
> for stats and you can shave say 32B per rule - it is not a big
> deal if you have a few rules. If you have 1M rules thats 32MB/s
> removed.
> So how do you get the stats? You can poll the rules (which have actions
> that embed the stats). That approach is taken by Ovs and some others.
> Or you can poll the actions instead (approach we have taken to cut
> further on data crossing). Polling the actions has also got a lot of
> other features built in for this precise purpose (example time-of-use
> filtering).
> Terse is useful in both cases because it cuts the amount of data
> further.

Ack.