netdev - Re: [PATCH bpf-next 1/3] dev: Move received_rps counter next to RPS members in softnet data

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Date:   Fri, 19 Aug 2022 15:54:21 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/3] dev: Move received_rps counter next to RPS
 members in softnet data

On Fri, 19 Aug 2022 14:38:14 +0200 Toke Høiland-Jørgensen wrote:
> Jakub Kicinski <kuba@...nel.org> writes:
> > On Thu, 18 Aug 2022 18:59:03 +0200 Toke Høiland-Jørgensen wrote:  
> >> Move the received_rps counter value next to the other RPS-related members
> >> in softnet_data. This closes two four-byte holes in the structure, making
> >> room for another pointer in the first two cache lines without bumping the
> >> xmit struct to its own line.  
> >
> > What's the pointer you're making space for (which I hope will explain
> > why this patch is part of this otherwise bpf series)?  
> 
> The XDP queueing series adds a pointer to keep track of which interfaces
> were scheduled for transmission using the XDP dequeue hook (similar to
> how the qdisc wake code works):
> 
> https://lore.kernel.org/r/20220713111430.134810-12-toke@redhat.com

I see, it makes more sense now :)

> Note that it's still up in the air if this ends up being the way this
> will be implemented, so I'm OK with dropping this patch for now if you'd
> rather wait until it's really needed. OTOH it also seemed like a benign
> change on its own, so I figured I might as well include this patch when
> sending these out. WDYT?

Whatever is easiest :)