netdev - Re: [PATCH net-next 07/11] net: fec: use switch statement to check the type of tx

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Message-ID: <20260114134713.565f2b3c@pumpkin>
Date: Wed, 14 Jan 2026 13:47:13 +0000
From: David Laight <david.laight.linux@...il.com>
To: Wei Fang <wei.fang@....com>
Cc: shenwei.wang@....com, xiaoning.wang@....com, frank.li@....com,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, ast@...nel.org, daniel@...earbox.net,
 hawk@...nel.org, john.fastabend@...il.com, sdf@...ichev.me,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, imx@...ts.linux.dev,
 bpf@...r.kernel.org
Subject: Re: [PATCH net-next 07/11] net: fec: use switch statement to check
 the type of tx_buf

On Tue, 13 Jan 2026 11:29:35 +0800
Wei Fang <wei.fang@....com> wrote:

> The tx_buf has three types: FEC_TXBUF_T_SKB, FEC_TXBUF_T_XDP_NDO and
> FEC_TXBUF_T_XDP_TX. Currently, the driver uses 'if...else...' statements
> to check the type and perform the corresponding processing. This is very
> detrimental to future expansion. For example, if new types are added to
> support XDP zero copy in the future, continuing to use 'if...else...'
> would be a very bad coding style. So the 'if...else...' statements in
> the current driver are replaced with switch statements to support XDP
> zero copy in the future.

The if...else... sequence has the advantage that the common 'cases'
can be put first.
The compiler will use a branch tree for a switch statement (jumps tables
are pretty much not allowed because of speculative execution issues) and
limit the maximum number of branches.
That is likely to be pessimal in many cases - especially if it generates
mispredicted branches for the common cases.

So not clear cut at all.

	David