Messages in this thread | | | Date | Wed, 18 Sep 2019 11:39:19 -0500 | From | Segher Boessenkool <> | Subject | Re: [PATCH v3 2/2] powerpc/irq: inline call_do_irq() and call_do_softirq() |
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Hi Christophe,
On Wed, Sep 18, 2019 at 03:48:20PM +0000, Christophe Leroy wrote: > call_do_irq() and call_do_softirq() are quite similar on PPC32 and > PPC64 and are simple enough to be worth inlining. > > Inlining them avoids an mflr/mtlr pair plus a save/reload on stack.
But you hardcode the calling sequence in inline asm, which for various reasons is not a great idea.
> +static inline void call_do_irq(struct pt_regs *regs, void *sp) > +{ > + register unsigned long r3 asm("r3") = (unsigned long)regs; > + > + asm volatile( > + " "PPC_STLU" 1, %2(%1);\n" > + " mr 1, %1;\n" > + " bl %3;\n" > + " "PPC_LL" 1, 0(1);\n" : "+r"(r3) : > + "b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), "i"(__do_irq) : > + "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7", > + "r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12"); > +}
I realise the original code had this... Loading the old stack pointer value back from the stack creates a bottleneck (via the store->load forwarding it requires). It could just use addi 1,1,-(%2) here, which can also be written as addi 1,1,%n2 (that is portable to all architectures btw).
Please write the "+r"(r3) on the next line? Not on the same line as the multi-line template. This make things more readable.
I don't know if using functions as an "i" works properly... It probably does, it's just not something that you see often :-)
What about r2? Various ABIs handle that differently. This might make it impossible to share implementation between 32-bit and 64-bit for this. But we could add it to the clobber list worst case, that will always work.
So anyway, it looks to me like it will work. Nice cleanup. Would be better if you could do the call to __do_irq from C code, but maybe we cannot have everything ;-)
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Segher
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