On Tue, Nov 15, 2016 at 02:19:53PM +0100, Christian Borntraeger wrote: > On 11/15/2016 01:30 PM, Russell King - ARM Linux wrote: > > On Tue, Oct 25, 2016 at 11:03:11AM +0200, Christian Borntraeger wrote: > >> For spinning loops people do often use barrier() or cpu_relax(). > >> For most architectures cpu_relax and barrier are the same, but on > >> some architectures cpu_relax can add some latency. > >> For example on power,sparc64 and arc, cpu_relax can shift the CPU > >> towards other hardware threads in an SMT environment. > >> On s390 cpu_relax does even more, it uses an hypercall to the > >> hypervisor to give up the timeslice. > >> In contrast to the SMT yielding this can result in larger latencies. > >> In some places this latency is unwanted, so another variant > >> "cpu_relax_lowlatency" was introduced. Before this is used in more > >> and more places, lets revert the logic and provide a cpu_relax_yield > >> that can be called in places where yielding is more important than > >> latency. By default this is the same as cpu_relax on all architectures. > > > > Rather than having to update all these architectures in this way, can't > > we put in some linux/*.h header something like: > > > > #ifndef cpu_relax_yield > > #define cpu_relax_yield() cpu_relax() > > #endif > > > > so only those architectures that need to do something need to be > > modified? > > These patches are part of linux-next since a month or so, changing that > would invalidate all the next testing. If people want that, I can certainly > do that, though. It's three weeks since you posted them. For one of those weeks (the week you posted them) I was away, and missed them while catching up. Sorry, but it sometimes takes a while to spot things amongst the backlog, and normally takes some subsequent activity on the thread to bring it back into view. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
