Re: [dpdk-dev] Forcing inlining for igb_uio and kni

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Jun 11, 2019 at 07:25:09AM -0700, Stephen Hemminger wrote:
> On Tue, 11 Jun 2019 11:18:22 +0100
> Bruce Richardson <bruce.richardson@intel.com> wrote:
> 
> > On Tue, Jun 11, 2019 at 11:44:01AM +0200, David Marchand wrote:
> > >    On Tue, Jun 11, 2019 at 11:31 AM Ilya Maximets
> > >    <[1]i.maximets@samsung.com> wrote:
> > > 
> > >      On 11.06.2019 11:45, David Marchand wrote:  
> > >      > I noticed that OVS CI [1] patches the dpdk sources to force some  
> > >      inlining parameters and get kni and igb_uio to build fine.  
> > >      >
> > >      > Looking at it in dpdk, meson support dropped this.
> > >      > In the makefiles, I can't find a reason in the git history (we go  
> > >      back to 1.3.0rX version).  
> > >      >
> > >      > [dmarchan@dmarchan dpdk]$ git grep max-inline-insns-single
> > >      > kernel/linux/igb_uio/Makefile:MODULE_CFLAGS += -I$(SRCDIR) --param  
> > >      max-inline-insns-single=100  
> > >      > kernel/linux/kni/Makefile:MODULE_CFLAGS += -I$(SRCDIR) --param  
> > >      max-inline-insns-single=50  
> > >      > [dmarchan@dmarchan dpdk]$ git blame origin/master --  
> > >      kernel/linux/igb_uio/Makefile |grep max-inline-insns-single  
> > >      > 13dc56a6 lib/librte_eal/linuxapp/igb_uio/Makefile (Intel  
> > >       2012-12-20 00:00:00 +0100 15) MODULE_CFLAGS += -I$(SRCDIR) --param
> > >      max-inline-insns-single=100  
> > >      > [dmarchan@dmarchan dpdk]$ git blame origin/master --  
> > >      kernel/linux/kni/Makefile |grep max-inline-insns-single  
> > >      > 3fc5ca2f lib/librte_eal/linuxapp/kni/Makefile (Intel  
> > >      2012-12-20 00:00:00 +0100 14) MODULE_CFLAGS += -I$(SRCDIR) --param
> > >      max-inline-insns-single=50  
> > >      >
> > >      > Is there a valid reason to keep this?
> > >      > 1:  
> > >      [2]https://github.com/openvswitch/ovs/blob/master/.travis/linux-buil
> > >      d.sh#L81
> > >      <[3]https://protect2.fireeye.com/url?k=b7de159c45b1fa79.b7df9ed3-c48
> > >      06461f28ecaf5&u=https://github.com/openvswitch/ovs/blob/master/.trav
> > >      is/linux-build.sh#L81>
> > >      Hi, David.
> > >      I don't know the reason for these in OVS travis config, But we don't
> > >      need to know them, actually. I have a patch to drop all the kernel
> > >      related stuff from the DPDK build in OVS Travis checks, just didn't
> > >      send it yet. Will send soon, probably.
> > > 
> > >    I had this in mind since we don't need those kmods in the CI.
> > >    Thanks Ilya.
> > >    The question on dpdk side remains open :-).
> > >    --
> > >    David Marchand  
> > 
> > I know that previously we did have issues with the modules not compiling
> > due to errors about maximum levels of inlines. Whether that was because of
> > the compiler, or the kernel makefiles at the time, I'm not sure. The kmods
> > seem to build fine for me now without the parameters, and the fact that
> > there has never been a problem reported with building using meson either,
> > probably indicates that the extra compiler flags can be dropped.
> > 
> > /Bruce
> 
> I really doubt forcing inlining makes any difference to the performance.

I agree, especially for uio module. This was not a "perf" issue, but a
"just own't compile" issue, IIRC. :-)

That being said, given that this is just a line in two makefiles, the rule
about "if it ain't broke" may apply....