Re: [PATCH v3 1/3] testpmd: Do not enable mbuf fast release TX offload by default

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 5 Aug 2025 07:48:41 +0200
Morten Brørup <mb@smartsharesystems.com> wrote:

> > From: fengchengwen [mailto:fengchengwen@huawei.com]
> > Sent: Tuesday, 5 August 2025 02.59
> > 
> > On 8/4/2025 3:42 AM, Morten Brørup wrote:  
> > > Enabling some offload by default may conflict with a manually  
> > configured  
> > > offload.
> > > Specifically, the mbuf fast release TX offload, which conflicts with  
> > multi  
> > > segment packet TX offload, was enabled by default.
> > > Therefore, mbuf fast release TX offload (the only TX offload which was
> > > enabled by default) is not enabled by default anymore.  
> > 
> > This may impact default performance, many vendor performance report has
> > testpmd iofwd or macfwd case.  
> 
> Yes.
> 
> IMO, any optimizations, mbuf-fast-free or mbuf-recycle, must be explicitly enabled, and documented in the performance reports when used.
> Otherwise the performance reports give a false impression of higher performance, which is only available under certain circumstances.
> I have complained about this before.
> Which is also why mbuf-recycle must be explicitly enabled.
> With this patch, the same finally applies to mbuf-fast-free too.
> I could add a Fixes tag, but I think it is better to categorize this patch as an improvement rather than a bug fix.
> 

Agree that optimizations like this need to be opt-in.
Maybe ethdev should automatically downgrade rather than reject bad configurations.

The DPDK already has too many "benchmark special" tweaks.