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    SubjectRe: Loongson (and other $ARCHs?) idle VS timer enqueue
    On Sun, Apr 23, 2023 at 09:52:49PM +0800, bibo, mao wrote:
    >
    >
    > 在 2023/4/22 23:04, Peter Zijlstra 写道:
    > > On Sat, Apr 22, 2023 at 04:21:45PM +0200, Frederic Weisbecker wrote:
    > > > On Sat, Apr 22, 2023 at 10:17:00AM +0200, Peter Zijlstra wrote:
    > > > > diff --git a/arch/loongarch/kernel/genex.S b/arch/loongarch/kernel/genex.S
    > > > > index 44ff1ff64260..5a102ff80de0 100644
    > > > > --- a/arch/loongarch/kernel/genex.S
    > > > > +++ b/arch/loongarch/kernel/genex.S
    > > > > @@ -40,6 +40,7 @@ SYM_FUNC_START(handle_vint)
    > > > > ori t0, t0, 0x1f
    > > > > xori t0, t0, 0x1f
    > > > > bne t0, t1, 1f
    > > > > + addi.d t0, t0, 0x20
    > > > > LONG_S t0, sp, PT_ERA
    > > > > 1: move a0, sp
    > > > > move a1, sp
    > > >
    > > > But the interrupts are enabled in C from arch_cpu_idle(), which
    > > > only then calls the ASM __arch_cpu_idle(). So if the interrupt happens
    > > > somewhere in between the call, the rollback (or fast-forward now)
    > > > doesn't apply.
    > I do not know much details about scheduler and timer, if the interrupt
    > happens between the call, will flag _TIF_NEED_RESCHED be set? If it is set,
    > the rollback will still apply.

    Nop, TIF_NEED_RESCHED is set only if a task is ready to run after the interrupt,
    not if the interrupt only modified/added a timer.

    > > @@ -40,6 +40,7 @@ SYM_FUNC_START(handle_vint)
    > > ori t0, t0, 0x1f
    > > xori t0, t0, 0x1f
    > > bne t0, t1, 1f
    > > + addi.d t0, t0, 0x20
    > It is more reasonable with this patch, this will jump out of idle function
    > directly after interrupt returns. If so, can we remove checking
    > _TIF_NEED_RESCHED in idle ASM function?

    Indeed we can remove the check to TIF_RESCHED!

    Thanks!

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