Re: [PATCH 7/8] tcp_splice: Remove questionable "optimisation" of pending bytes tracking

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jun 04, 2026 at 06:41:43AM +0200, Stefano Brivio wrote:
> On Thu, 28 May 2026 15:02:12 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > We have a special path that avoids updating conn->pending when the amounts
> > read and written are equal.  This has a conceptual complexity cost, in
> > particular, it means that conn->pending[] is not accurate to its normal
> > meaning for a section of the loop body.
> > 
> > conn->pending[] shares a cacheline with conn->pipe[] and conn->s[], so it's
> > almost certainly cache-hot.  It's questionable that avoiding the update
> > of pending even outweighs the extra conditional branch, let alone saves
> > anything of significance.  Remove it.
> 
> I added this when we still had 64-bit counters, that is, two weeks
> before commit 37c228ada88b ("tap, tcp, udp, icmp: Cut down on some
> oversized buffers"), but now, as you point out, it doesn't make sense anymore.

Ah, that makes some sense.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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