On Thu, 15 Oct 2020 19:14:48 +0200 Thomas Monjalon <tho...@monjalon.net> wrote:
> 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. > > I assume only some Rx/Tx functions are impacted. > We probably need such disabling option per-file. > > > However, at this point, I think we need a little more investigation. Is > > there any testing you can do to see if it's just in your driver, or in > > perhaps a mempool driver/lib that the issue appears, or if it's just a > > global slowdown? Do you see the impact with both clang and gcc? I'll > > retest things a bit tomorrow on my end to see what I see. > > Yes we need to know which libs or files are impacted by -fPIC. The issue is that all shared libraries need to be built with PIC. So it is a question of static vs shared library build.
