On Thu, 28 May 2015, Jason Gunthorpe wrote: > Second: What about wrap around? Does it even make sense to expose less > than 64 bits to userspace? Should the driver manage wrap around to > create a flat 64 bit space?
The wrap around is given by the mask. Cycle registers are often shorter than 64 bits. > Otherwise, if the app has to do it, there is no event indicating wrap > has occured. Well yes. You take the difference and then apply the mask. If you are outside of the cycle range then this will not give you a proper time. > Without managing wrapping, cycle count difference is not a reliable > calculation. Counters only works for the interval in which they do not go through a complete cycle. But that is the nature of these counters. And thats what you see when you look into the kernel timer subsystem for example. > > This is not only for Ethernet. Internally Infiniband is frequently used > > and there also timestamps are useful. > > Sure, but should any other vendors be commenting on this UAPI? I think they would have spoken up if they had any objections? -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
