On Thu, Jan 05, 2017 at 01:31:44PM +0800, Jianbo Liu wrote: > On 4 January 2017 at 18:01, Jerin Jacob <jerin.ja...@caviumnetworks.com> > wrote: > > On Tue, Jan 03, 2017 at 03:48:32PM +0800, Jianbo Liu wrote: > >> On 27 December 2016 at 17:49, Jerin Jacob > >> <jerin.ja...@caviumnetworks.com> wrote: > >> > CC: Jianbo Liu <jianbo....@linaro.org> > >> > Signed-off-by: Jerin Jacob <jerin.ja...@caviumnetworks.com> > >> > --- > >> > lib/librte_eal/common/include/arch/arm/rte_atomic_64.h | 6 ++++++ > >> > 1 file changed, 6 insertions(+) > >> > > >> > diff --git a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h > >> > b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h > >> > index 78ebea2..ef0efc7 100644 > >> > --- a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h > >> > +++ b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h > >> > @@ -88,6 +88,12 @@ static inline void rte_rmb(void) > >> > > >> > #define rte_smp_rmb() dmb(ishld) > >> > > >> > +#define rte_io_mb() rte_mb() > >> > + > >> > +#define rte_io_wmb() rte_wmb() > >> > + > >> > +#define rte_io_rmb() rte_rmb() > >> > + > >> > >> I think it's better to use outer shareable dmb for io barrier, instead of > >> dsb. > > > > Its is difficult to generalize. AFAIK, from the IO barrier perspective > > dsb would be the right candidate. But just for the DMA barrier between IO > > may > > be outer sharable dmb is enough. In-terms of performance implication, the > > fastpath code(door bell write) has been changed to relaxed write in all > > the drivers in this patchset and rte_io_* will be only > > used by rte_[read/write]8/16/32/64 which will be in slow-path. > > So, IMO, it better stick with dsb and its safe from the complete IO barrier > > perspective. > > If so, why not use *mb() directly?
Adding David Marchand, EAL Maintainer. Instead of rte_io_?. I thought, IO specific constraints can be abstracted here in rte_io_*. Apart from arm, there other arch like "arc" has similar constraints. IMHO, no harm in keeping that abstraction. Thoughts ? http://lxr.free-electrons.com/ident?i=__iormb > > > > > At least on ThunderX, I couldn't see any performance difference between > > using dsb(st) and dmb(oshst) for dma write barrier before the doorbell > > register > > write in fastpath. In case there are platforms which has such performance > > difference, > > may be could add rte_dma_wmb() and rte_dma_rmb() in future like Linux kernel > > dma_wmb() and dma_rmb().(But i couldn't see all the driver are using it, > > though) > > > > But there is no io_*mb() in the kernel, so you want to be different? It is their for arm,arm64,arc architectures in Linux kernel. Please check writel implementation for arm64 http://lxr.free-electrons.com/source/arch/arm64/include/asm/io.h#L143
