> -----Original Message----- > From: Thomas Monjalon <tho...@monjalon.net> > Sent: Sunday, April 26, 2020 1:18 AM > To: Phil Yang <phil.y...@arm.com> > Cc: erik.g.carri...@intel.com; rsanf...@akamai.com; dev@dpdk.org; > david.march...@redhat.com; Honnappa Nagarahalli > <honnappa.nagaraha...@arm.com>; Gavin Hu <gavin...@arm.com>; nd > <n...@arm.com> > Subject: Re: [dpdk-dev] [PATCH v3] lib/timer: relax barrier for status update > > 24/04/2020 09:24, Phil Yang: > > Volatile has no ordering semantics. The rte_timer structure defines > > timer status as a volatile variable and uses the rte_r/wmb barrier > > to guarantee inter-thread visibility. > > > > This patch optimized the volatile operation with c11 atomic operations > > and one-way barrier to save the performance penalty. According to the > > timer_perf_autotest benchmarking results, this patch can uplift 10%~16% > > timer appending performance, 3%~20% timer resetting performance and > 45% > > timer callbacks scheduling performance on aarch64 and no loss in > > performance for x86. > > > > Suggested-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com> > > Signed-off-by: Phil Yang <phil.y...@arm.com> > > Reviewed-by: Gavin Hu <gavin...@arm.com> > > Acked-by: Erik Gabriel Carrillo <erik.g.carri...@intel.com> > [...] > > --- a/lib/librte_timer/rte_timer.h > > +++ b/lib/librte_timer/rte_timer.h > > @@ -101,7 +101,7 @@ struct rte_timer > > - volatile union rte_timer_status status; /**< Status of timer. */ > > + union rte_timer_status status; /**< Status of timer. */ > > Unfortunately, I cannot merge this patch because it breaks the ABI: > > [C]'function void rte_timer_init(rte_timer*)' at rte_timer.c:214:1 has some > indirect sub-type changes: > parameter 1 of type 'rte_timer*' has sub-type changes: > in pointed to type 'struct rte_timer' at rte_timer.h:100:1: > type size hasn't changed > 1 data member changes (2 filtered): > type of 'volatile rte_timer_status rte_timer::status' changed: > entity changed from 'volatile rte_timer_status' to 'union > rte_timer_status' at rte_timer.h:67:1 > type size hasn't changed >
I think we can revert it to the original definition of rte_timer and keep the union rte_timer_status volatile-qualified. Because with or without this 'volatile' qualify, it generates the same code on aarch64 and x86. So it seems acceptable to ignore it to make the ABI compatible? Thank, Phil
