Re: Loongson (and other $ARCHs?) idle VS timer enqueue

[WANG Xuerui]

On 2023/4/26 08:46, maobibo wrote:
> 在 2023/4/25 21:28, WANG Xuerui 写道:
> > On 2023/4/25 21:25, maobibo wrote:
> > > 在 2023/4/25 19:49, Peter Zijlstra 写道:
> >
> > <snip>
> >
> > > > diff --git a/arch/loongarch/kernel/genex.S b/arch/loongarch/kernel/genex.S
> > > > index 44ff1ff64260..3c8a6bab98fe 100644
> > > > --- a/arch/loongarch/kernel/genex.S
> > > > +++ b/arch/loongarch/kernel/genex.S
> > > > @@ -18,27 +18,31 @@
> > > >          .align    5
> > > >    SYM_FUNC_START(__arch_cpu_idle)
> > > > -    /* start of rollback region */
> > > > -    LONG_L    t0, tp, TI_FLAGS
> > > > -    nop
> > > > -    andi    t0, t0, _TIF_NEED_RESCHED
> > > > -    bnez    t0, 1f
> > > > -    nop
> > > > -    nop
> > > > -    nop
> > > > +    /* start of idle interrupt region */
> > > > +    move    t0, CSR_CRMD_IE
> > > addi.d  t0, zero, CSR_CRMD_IE can be used here, move is used for reg to reg
> >
> > Or better: li.d t0, CSR_CRMD_IE (prefer pseudo-instruction over concrete ones whenever it helps readability). We don't need to support ancient in-house toolchains without support for even li. ;-)
>    
> I am not familiar with compiler:(, how many actual instructions does
> pseudo-instr li.d takes? It will be ok if it uses only one intr, else
> there will be problem.

It's just `ori $t0, $zero, 4` no matter which of li.w or li.d is used. 
It only matters when the immediate to load is bigger. Given CSR_CRMD_IE 
is just 4 (1<<2) you can definitely say `li.w` if you want to be extra 
cautious and it won't hurt. ;-)

--
WANG "xen0n" Xuerui

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