On Fri, 2011-03-04 at 16:22 -0600, Tseng-Hui (Frank) Lin wrote: > > Well, I don't know how you use icswx on P7+, but on Prism it's > > definitely issued directly by userspace. > > > OK. You've got a point. I wasn't aware of Prism. HFI device driver is > currently the only icswx user on P7. Could you point me to more > information about how Prism uses icswx from user space?
Let's ignore that for now, there's a whole infrastructure for it and it hasn't been published yet, maybe later this year... We can look at exposing the feature to userspace then. > > You don't need to. You allocate and initialize the structure, and you > > compare & swap the pointer. If somebody beat you, you trash your copy. > > > Is atomic_cmpxchg() the one to do the trick? No, just cmpxchg() > The lazy switching checks the shadow variable first before setting ACOP > register. This saves mtspr() only if the new value is the same as > current. If there are several coprocessors on the system, the ACOP > register may have to be changed frequently. In that case, the lazy > switching will not save time. In extreme case when the ACOP register > needs to be changed every time, it actually slows down the execution by > the additional shadow variable checking. By how much ? Is it even measurable ? Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
