netdev - Re: [PATCH RFC bpf-next 06/20] trait: Replace memmove calls with inline move

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Message-ID: <529122c4-a704-4d3a-8ec0-98552e7a87a2@kernel.org>
Date: Thu, 6 Mar 2025 11:14:33 +0100
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: arthur@...hurfabre.com, netdev@...r.kernel.org, bpf@...r.kernel.org
Cc: jakub@...udflare.com, yan@...udflare.com, jbrandeburg@...udflare.com,
 thoiland@...hat.com, lbiancon@...hat.com,
 Arthur Fabre <afabre@...udflare.com>
Subject: Re: [PATCH RFC bpf-next 06/20] trait: Replace memmove calls with
 inline move



On 05/03/2025 15.32, arthur@...hurfabre.com wrote:
> From: Arthur Fabre <afabre@...udflare.com>
> 
> When inserting or deleting traits, we need to move any subsequent
> traits over.
> 
> Replace it with an inline implementation to avoid the function call
> overhead. This is especially expensive on AMD with SRSO.
> 
> In practice we shouldn't have too much data to move around, and we're
> naturally limited to 238 bytes max, so a dumb implementation should
> hopefully be fast enough.
> 
> Jesper Brouer kindly ran benchmarks on real hardware with three configs:
> - Intel: E5-1650 v4
> - AMD SRSO: 9684X SRSO
> - AMD IBPB: 9684X SRSO=IBPB
> 
> 		Intel	AMD IBPB	AMD SRSO
> xdp-trait-get	5.530	3.901		9.188		(ns/op)
> xdp-trait-set	7.538	4.941		10.050		(ns/op)
> xdp-trait-move	14.245	8.865		14.834		(ns/op)
> function call	1.319	1.359		5.703		(ns/op)
> indirect call	8.922	6.251		10.329		(ns/op)
> 

I've done extensive *micro* bechmarking documented here:
  - https://github.com/xdp-project/xdp-project/tree/main/areas/hints
  - In traits0X_* files

The latest that corresponds to this patchset is in this file:
  - 
https://github.com/xdp-project/xdp-project/blob/main/areas/hints/traits07_bench-009.org

I've not done XDP_REDIRECT testing, which would likely show the bitfield 
change in xdp_frame, that Olek pointed out.

--Jesper