Hi Thomas,
On Wed, 1 Feb 2023, Thomas Monjalon wrote:
01/02/2023 11:58, Andrew Rybchenko:
On 2/1/23 13:48, Jerin Jacob wrote:
On Wed, Feb 1, 2023 at 2:59 PM Andrew Rybchenko
<andrew.rybche...@oktetlabs.ru> wrote:
Frankly speaking I don't understand why default value is so
important if we have a way to change it. Reasons should be
really strong to change existing defaults.
The only reason is, typically testpmd will be used performance
benchmarking as an industry standard. It is difficult to tell/educate
the QA or customers
that, "BTW if you need to get better performance add more flag to
testpmd command line".
I disagree.
When you do performance benchmark, you tune settings accordingly.
To make that worst, only some PMD needs to give the additional
parameter to get better number.
And also, testpmd usage will be treated as application modeling.
Since this feature only used on sfc and cnxk driver, What is the
situation with sfc driver?
Keeping it as negotiated and not use the feature, will impact the per
core performance of sfc or
is it just PCI bandwidth thing which really dont show any difference in testpmd?
Yes, sfc could run faster if no Rx metadata are negotiated. So,
it is better to negotiate nothing by default. But it is always
painful to change defaults. You need to explain that now you
need to negotiate Rx metadata to use mark, flag and tunnel offloads.
Yes, it will be required on sfc and cnxk only.
As an sfc maintainer I don't mind to change testpmd defaults.
If we change testpmd defaults to "do nothing",
then we should disable MBUF_FAST_FREE as well.
No. These are completely different. MBUF_FAST_FREE is an
optimisation technique, it's in the offload namespace.
Whilst "negotiate metadata" does not offload anything.
It just tells the PMD to enable *delivery* of some
data *when it is present*. And whether it will be
present or not, - this is decided by flow actions.
And, flow actions, in turn, belong in the domain
of decisions made by a specific person operating
the application. So no need to remove FAST_FREE.
