On Tue, 2016-02-23 at 13:04 +1100, Michael Ellerman wrote: > On Tue, 2016-02-16 at 15:21 -0600, Scott Wood wrote: > > > On Thu, 2016-02-11 at 17:16 +0100, Christophe Leroy wrote: > > > > This patch provides VIRT_CPU_ACCOUTING to PPC32 architecture. > > > PPC32 doesn't have the PACA structure, so we use the task_info > > > structure to store the accounting data. > > > > > > In order to reuse on PPC32 the PPC64 functions, all u64 data has > > > been replaced by 'unsigned long' so that it is u32 on PPC32 and > > > u64 on PPC64 > > > > > > Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr> > > > --- > > > Changes in v3: unlike previous version of the patch that was inspired > > > from IA64 architecture, this new version tries to reuse as much as > > > possible the PPC64 implementation. > > > > > > PPC32 doesn't have PACA and past discusion on v2 version has shown > > > that it is not worth implementing a PACA in PPC32 architecture > > > (see below benh opinion) > > > > > > benh: PACA is actually a data structure and you really really don't want > > > it > > > on ppc32 :-) Having a register point to current works, having a register > > > point to per-cpu data instead works too (ie, change what we do today), > > > but don't introduce a PACA *please* :-) > > > > And Ben never replied to my reply at the time: > > > > "What is special about 64-bit that warrants doing things differently from > > 32 > > -bit? > > Nothing. It's just historical cruft. But we're not realistically going to > get > rid of it anytime soon on 64-bit.
I wasn't suggesting getting rid of it on 64-bit, but rather adding it on 32 -bit, to hold things that are used by both. I was confused by the vehemence of Ben's objection. > > What is the difference between PACA and "per-cpu data", other than the > > obscure name?" > > Not much. The pacas are allocated differently to per-cpu data, they're > available earlier in boot etc. Ah, I was thinking of the general concept of per-cpu data, not the specific mechanism that Linux implements in percpu.h etc. > What we'd like is to have r13 point to the > per-cpu data area, and then the contents of the paca could just be regular > per-cpu data. But like I said above that's a big change. That change seems orthogonal to the question of making the mechanism available on 32-bit to ease unification of code which uses it. -Scott _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
