> -----Original Message----- > From: Stephen Hemminger <step...@networkplumber.org> > Sent: Thursday, April 29, 2021 11:06 PM > To: Ruifeng Wang <ruifeng.w...@arm.com> > Cc: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>; Konstantin > Ananyev <konstantin.anan...@intel.com>; dev@dpdk.org; > david.march...@redhat.com; tho...@monjalon.net; jer...@marvell.com; > nd <n...@arm.com>; Gavin Hu <gavin...@arm.com>; Steve Capper > <steve.cap...@arm.com>; Ola Liljedahl <ola.liljed...@arm.com> > Subject: Re: [dpdk-dev] [PATCH v3 2/2] ring: use wfe to wait for ring tail > update on aarch64 > > On Thu, 29 Apr 2021 14:35:35 +0000 > Ruifeng Wang <ruifeng.w...@arm.com> wrote: > > > > -----Original Message----- > > > From: Stephen Hemminger <step...@networkplumber.org> > > > Sent: Thursday, April 29, 2021 1:17 AM > > > To: Ruifeng Wang <ruifeng.w...@arm.com> > > > Cc: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>; Konstantin > > > Ananyev <konstantin.anan...@intel.com>; dev@dpdk.org; > > > david.march...@redhat.com; tho...@monjalon.net; > jer...@marvell.com; > > > nd <n...@arm.com>; Gavin Hu <gavin...@arm.com>; Steve Capper > > > <steve.cap...@arm.com>; Ola Liljedahl <ola.liljed...@arm.com> > > > Subject: Re: [dpdk-dev] [PATCH v3 2/2] ring: use wfe to wait for > > > ring tail update on aarch64 > > > > > > On Sun, 25 Apr 2021 05:56:53 +0000 > > > Ruifeng Wang <ruifeng.w...@arm.com> wrote: > > > > > > > Instead of polling for tail to be updated, use wfe instruction. > > > > > > > > Signed-off-by: Gavin Hu <gavin...@arm.com> > > > > Signed-off-by: Ruifeng Wang <ruifeng.w...@arm.com> > > > > Reviewed-by: Steve Capper <steve.cap...@arm.com> > > > > Reviewed-by: Ola Liljedahl <ola.liljed...@arm.com> > > > > Reviewed-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com> > > > > Acked-by: Konstantin Ananyev <konstantin.anan...@intel.com> > > > > > > Looks ok to me, but it does raise an interesting question. > > > Shouldn't the original code have been using atomic load to look at > > > ht->tail. > > > > > > This another place where "volatile considered harmful" applies. > > > > Do you mean 'volatile' should be removed from rte_wait_until_equal_xxx > parameters? > > > > I meant that all access to tail should be via C11 atomic builtin. At that > point, > the volatile on the data structure elements does not matter.
Agreed. If synchronization is ensured by using C11 atomic builtin, 'volatile' on elements can be removed.
