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? > > 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?
