On Thu, May 28, 2015 at 03:34:00PM -0500, Christoph Lameter wrote: > 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.
I am aware of how cycle counters work. My point was exposing raw wrapping counters is a horrible UAPI. Shouldn't the driver software extend smaller counters to 64 bits? That would take a single or and an unlikely branch, so don't say 'performance' :) > 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. Very little in the kernel is exposed to that wrapping, the timer subsystem takes care of it. Certainly, userspace never sees it. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
