Re: [dpdk-dev] [dpdk-stable] [PATCH v4] mbuf: fix reset on mbuf free

[Thomas Monjalon <thomas@monjalon.net>]

30/07/2021 16:35, Morten Brørup:
> > From: Olivier Matz [mailto:olivier.matz@6wind.com]
> > Sent: Friday, 30 July 2021 14.37
> > 
> > Hi Thomas,
> > 
> > On Sat, Jul 24, 2021 at 10:47:34AM +0200, Thomas Monjalon wrote:
> > > What's the follow-up for this patch?
> > 
> > Unfortunatly, I still don't have the time to work on this topic yet.
> > 
> > In my initial tests, in our lab, I didn't notice any performance
> > regression, but Ali has seen an impact (0.5M PPS, but I don't know how
> > much in percent).
> > 
> > 
> > > 19/01/2021 15:04, Slava Ovsiienko:
> > > > Hi, All
> > > >
> > > > Could we postpose this patch at least to rc2? We would like to
> > conduct more investigations?
> > > >
> > > > With best regards, Slava
> > > >
> > > > From: Olivier Matz <olivier.matz@6wind.com>
> > > > > On Mon, Jan 18, 2021 at 05:52:32PM +0000, Ali Alnubani wrote:
> > > > > > Hi,
> > > > > > (Sorry had to resend this to some recipients due to mail server
> > problems).
> > > > > >
> > > > > > Just confirming that I can still reproduce the regression with
> > single core and
> > > > > 64B frames on other servers.
> > > > >
> > > > > Many thanks for the feedback. Can you please detail what is the
> > amount of
> > > > > performance loss in percent, and confirm the test case? (I
> > suppose it is
> > > > > testpmd io forward).
> > > > >
> > > > > Unfortunatly, I won't be able to spend a lot of time on this soon
> > (sorry for
> > > > > that). So I see at least these 2 options:
> > > > >
> > > > > - postpone the patch again, until I can find more time to analyze
> > > > >   and optimize
> > > > > - apply the patch if the performance loss is acceptable compared
> > to
> > > > >   the added value of fixing a bug
> > > > >
> > > [...]
> > 
> > Statu quo...
> > 
> > Olivier
> > 
> 
> The decision should be simple:
> 
> Does the DPDK project support segmented packets?
> If yes, then apply the patch to fix the bug!
> 
> If anyone seriously cares about the regression it introduces, optimization patches are welcome later. We shouldn't wait for it.

You're right, but the regression is flagged to a 4-years old patch,
that's why I don't consider it as urgent.

> If the patch is not applied, the documentation must be updated to mention that we are releasing DPDK with a known bug: that segmented packets are handled incorrectly in the scenario described in this patch.

Yes, would be good to document the known issue,
no matter how old it is.

> Generally, there could be some performance to gain by not supporting segmented packets at all, as a compile time option. But that is a different discussion.
> 
> 
> -Morten