> -----Original Message----- > From: Bruce Richardson <bruce.richard...@intel.com> > Sent: Friday, April 30, 2021 10:19 PM > To: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com> > Cc: tho...@monjalon.net; Ruifeng Wang <ruifeng.w...@arm.com>; David > Marchand <david.march...@redhat.com>; dev <dev@dpdk.org>; > jer...@marvell.com; nd <n...@arm.com> > Subject: Re: Use WFE for spinlock and ring > > On Fri, Apr 30, 2021 at 01:41:22PM +0000, Honnappa Nagarahalli wrote: > > <snip> > > > > > > > > > > > > > > > > > > > > The rte_wait_until_equal_xxx APIs abstract the > > > > > > > > > functionality of 'polling for a memory location to > > > > > > > > > become equal to a given > > > value'[1]. > > > > > > > > > > > > > > > > > > Use the API for the rte spinlock and ring implementations. > > > > > > > > > With the wait until equal APIs being stable, changes > > > > > > > > > will not impact > > > ABI. > > > > > > > > > > > > > > > > Afaics, there is no ARM target with WFE enabled and we > > > > > > > > lost ability to enable WFE support with removal of the > > > > > > > > make build > > > system. > > > > > > > > > > > > > > WFE can be enabled with direct meson file change. > > > > > > > WFE is not intended to be enabled by default. It can be > > > > > > > enabled based on benchmarking result on hardware. > > > > > > > > > > > > > > > > $ git grep RTE_ARM_USE_WFE > > > > > > > > config/arm/meson.build: ['RTE_ARM_USE_WFE', false], > > > > > > > > lib/eal/arm/include/rte_pause_64.h:#ifdef RTE_ARM_USE_WFE > > > > > > > > > > > > > > > > How did you enable WFE to test this series? > > > > > > > > > > > > > > I modified meson file to test. > > > > > > > Tests were also done with WFE disabled to make sure no > > > > > > > degradation with > > > > > > generic implementation. > > > > > > > > > > > > I don't understand the usage. > > > > > > Which platform should use it? > > > > > > > > > > Platforms that implement WFE semantic (e.g. N1) can use. > > > > > The user can enable this feature for power efficiency purpose. > > > > > But there is something to note as described in commit message > > > > > 1be7855d77 > > > when the API was introduced. > > > > > > > > > > > Should it be a compile-time option? > > > > > > > > > > Yes, it should be a compile-time option. > > > > > It can be configured via c_args meson option? > > > > > > > > +Cc Bruce for discussing how to enable such feature. > > > > > > > > The problem with c_args is that the application has no way to know. > > > > > > > Agree about c_args not being a great choice. Why does this need to > > > be a compile-time option? Can runtime support not be detected in > > > some manner? > > The problem is inconsistency in performance on different Arm platforms. > We had decided that each platform needs to enable it after some testing. > > Then it sounds like it does indeed need to be a build option. Does it need to > be added to the meson_options.txt, or can it just be specified in cross-files > and optionally via c_args?
Add it to the meson_options.txt is good as the option will be clearly exposed. My concern is more options (e.g. RTE_ARCH_ARM64_MEMCPY) need to be added in. Will the options bloat meson_options.txt?
