On Fri, Oct 16, 2020 at 2:00 PM Bruce Richardson <[email protected]> wrote: > > On Thu, Oct 15, 2020 at 05:28:10PM +0000, Jerin Jacob Kollanukkaran wrote: > > > -----Original Message----- > > > From: Thomas Monjalon <[email protected]> > > > Sent: Thursday, October 15, 2020 10:45 PM > > > To: Ali Alnubani <[email protected]>; Bruce Richardson > > > <[email protected]> > > > Cc: [email protected]; Asaf Penso <[email protected]>; > > > [email protected]; [email protected]; > > > [email protected]; [email protected]; Jerin Jacob > > > Kollanukkaran <[email protected]> > > > Subject: [EXT] Re: performance degradation with fpic > > > > > > External Email > > > > > > ---------------------------------------------------------------------- > > > 15/10/2020 19:08, Bruce Richardson: > > > > On Thu, Oct 15, 2020 at 04:00:44PM +0000, Ali Alnubani wrote: > > > > > We have been seeing in some cases that the DPDK forwarding > > > performance > > > > > is up to 9% lower when DPDK is built as static with meson compared > > > > > to a > > > > > build with makefiles. > > > > > > > > > > The same degradation can be reproduced with makefiles on older DPDK > > > > > releases when building with EXTAR_CFLAGS set to “-fPIC”, it can > > > > > also be > > > > > resolved in meson when passing “pic: false” to meson’s > > > > > static_library > > > > > call (more tweaking needs to be done to prevent building shared > > > > > libraries because this change breaks them). > > > [...] > > > > > Should we disable PIC in static builds? > > > > > > > > thanks for reporting, though it's strange that you see such a big > > > > impact. > > > > In my previous tests with i40e driver I never noticed a difference > > > > between make and meson builds, and I and some others here have been > > > > using meson builds for any performance work for over a year now. That > > > > being said let me reverify what I see on my end. > > > > > > > > In terms of solutions, disabling the -fPIC flag globally implies that > > > > we can no longer build static and shared libs from the same sources, > > > > so we would need to revert to doing either a static or a shared > > > > library build but not both. If the issue is limited to only some > > > > drivers or some cases, we can perhaps add in a build option to have > > > > no-fpic-static builds, to be used in a cases where it is problematic. > > > > We have seen this issue earlier. Our issue was, meson, getting more > > performance > > Than make build system(Based on different changeset). Initially we > > suspected fpic > > is playing role. Based on our understanding, It not is fpic issue per say, > > it is more > > of text section code alignment change was creating the issue. > > Typically it happen with very "fine" grained, prefetches in Rx and Tx > > routines, then > > All timing will get changed by radical change to text section by fpic. > > > > Out of interest, what range of performance difference did you see, because > the 9% reported is fairly massive, well beyond anything I would expect from > such a change?
We have seen up to 4% difference in per core/mpps.
