On 2017/05/22 12:00AM, Nicholas Piggin wrote: > I'd like to take over the r14 register for use as a per-cpu kernel > register similar to the way r13 is used for the paca. > > r14 being the last non-volatile register gcc allocates, appears with > about 0.5% the frequency as r31 in (static) instructions. I haven't > counted dynamically how many extra spills and fills that removing it > causes, but I should. My guess is the memory ops saved by using > it as a per-cpu variable will significantly outweigh the cost of > losing it as a general use register. > > This part of the patch is pretty mechanical. A couple of places (prom) > still have to use it, and I haven't quite understood the KVM code yet. > > Question is whether this approach seems okay, and whether we should do > the same for 64e. > > Thanks, > Nick > > ---
[snip] > diff --git a/arch/powerpc/net/bpf_jit32.h > b/arch/powerpc/net/bpf_jit32.h > index a8cd7e289ecd..52a30db033c1 100644 > --- a/arch/powerpc/net/bpf_jit32.h > +++ b/arch/powerpc/net/bpf_jit32.h > @@ -44,9 +44,11 @@ > * A register r4 > * X register r5 > * addr param r6 > - * r7-r10 scratch > - * skb->data r14 > - * skb headlen r15 (skb->len - skb->data_len) > + * scratch r7-r8 > + * skb headlen r9 (skb->len - skb->data_len) > + * skb->data r10 > + * fixed regs r13-r14 > + * unused r15 > * m[0] r16 > * m[...] ... > * m[15] r31 > @@ -58,8 +60,8 @@ > #define r_addr 6 > #define r_scratch1 7 > #define r_scratch2 8 > -#define r_D 14 > -#define r_HL 15 > +#define r_HL 9 > +#define r_D 10 You'll also need changes in the JIT code itself, at least in bpf_jit_build_prologue() and elsewhere -- some code expects r_D and r_HL to be NVRs. It's probably easier to just choose other NVRs here... > #define r_M 16 > > #ifndef __ASSEMBLY__ > diff --git a/arch/powerpc/net/bpf_jit_asm.S b/arch/powerpc/net/bpf_jit_asm.S > index 3dd9c43d40c9..5b06152052f6 100644 > --- a/arch/powerpc/net/bpf_jit_asm.S > +++ b/arch/powerpc/net/bpf_jit_asm.S > @@ -19,8 +19,8 @@ > * r3 skb > * r4,r5 A,X > * r6 *** address parameter to helper *** > - * r7-r10 scratch > - * r14 skb->data > + * r7-r9 scratch > + * r10 skb->data > * r15 skb headlen > * r16-31 M[] This doesn't match the updates to bpf_jit32.h. - Naveen
