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Message-ID: <CAAhV-H4icr=9cgD_doqeh2h9+2s3e5V1OeOy-j1oxaZiTW5jBw@mail.gmail.com>
Date: Wed, 15 May 2024 12:02:09 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Guo Ren <guoren@...nel.org>
Cc: Huacai Chen <chenhuacai@...ngson.cn>, Arnd Bergmann <arnd@...db.de>, loongarch@...ts.linux.dev,
linux-arch@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
Xuerui Wang <kernel@...0n.name>, Jiaxun Yang <jiaxun.yang@...goat.com>,
linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Add irq_work support via self IPIs
On Wed, May 15, 2024 at 11:21 AM Guo Ren <guoren@...nel.org> wrote:
>
> On Tue, May 14, 2024 at 7:14 PM Huacai Chen <chenhuacai@...nel.org> wrote:
> >
> > Hi, Ren,
> >
> > On Tue, May 14, 2024 at 6:11 PM Guo Ren <guoren@...nel.org> wrote:
> > >
> > > On Tue, May 14, 2024 at 3:32 PM Huacai Chen <chenhuacai@...ngson.cn> wrote:
> > > >
> > > > Add irq_work support for LoongArch via self IPIs. This make it possible
> > > > to run works in hardware interrupt context, which is a prerequisite for
> > > > NOHZ_FULL.
> > > >
> > > > Implement:
> > > > - arch_irq_work_raise()
> > > > - arch_irq_work_has_interrupt()
> > > >
> > > > Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> > > > ---
> > > > arch/loongarch/include/asm/hardirq.h | 3 ++-
> > > > arch/loongarch/include/asm/irq_work.h | 10 ++++++++++
> > > > arch/loongarch/include/asm/smp.h | 2 ++
> > > > arch/loongarch/kernel/paravirt.c | 6 ++++++
> > > > arch/loongarch/kernel/smp.c | 14 ++++++++++++++
> > > > 5 files changed, 34 insertions(+), 1 deletion(-)
> > > > create mode 100644 arch/loongarch/include/asm/irq_work.h
> > > >
> > > > diff --git a/arch/loongarch/include/asm/hardirq.h b/arch/loongarch/include/asm/hardirq.h
> > > > index d41138abcf26..1d7feb719515 100644
> > > > --- a/arch/loongarch/include/asm/hardirq.h
> > > > +++ b/arch/loongarch/include/asm/hardirq.h
> > > > @@ -12,11 +12,12 @@
> > > > extern void ack_bad_irq(unsigned int irq);
> > > > #define ack_bad_irq ack_bad_irq
> > > >
> > > > -#define NR_IPI 2
> > > > +#define NR_IPI 3
> > > >
> > > > enum ipi_msg_type {
> > > > IPI_RESCHEDULE,
> > > > IPI_CALL_FUNCTION,
> > > > + IPI_IRQ_WORK,
> > > > };
> > > >
> > > > typedef struct {
> > > > diff --git a/arch/loongarch/include/asm/irq_work.h b/arch/loongarch/include/asm/irq_work.h
> > > > new file mode 100644
> > > > index 000000000000..d63076e9160d
> > > > --- /dev/null
> > > > +++ b/arch/loongarch/include/asm/irq_work.h
> > > > @@ -0,0 +1,10 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > > +#ifndef _ASM_LOONGARCH_IRQ_WORK_H
> > > > +#define _ASM_LOONGARCH_IRQ_WORK_H
> > > > +
> > > > +static inline bool arch_irq_work_has_interrupt(void)
> > > > +{
> > > > + return IS_ENABLED(CONFIG_SMP);
> > > I think it is "return true," or it will cause the warning.
> > No, HZ_FULL depends on SMP, if you force to enable it on UP, the
> > timekeeping will boom.
> > On the other hand, let the function return true will cause build
> > errors, see commit d2f3acde3d52b3b351db09e2e2a5e581 ("riscv: Fix
> > irq_work when SMP is disabled").
> Sorry, I misunderstood.
>
> But it is not a build error. Quote:
Sorry, I misunderstood, too.
Huacai
>
> This was found while bringing up cpufreq on D1. Switching cpufreq
> governors was hanging on irq_work_sync().
>
> /*
> * Synchronize against the irq_work @entry, ensures the entry is not
> * currently in use.
> */
> void irq_work_sync(struct irq_work *work)
> {
> lockdep_assert_irqs_enabled();
> might_sleep();
>
> if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
> !arch_irq_work_has_interrupt()) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work),
> TASK_UNINTERRUPTIBLE);
> return;
> }
>
>
> >
> > Huacai
> >
> > >
> > > void __init tick_nohz_init(void)
> > > {
> > > int cpu, ret;
> > >
> > > if (!tick_nohz_full_running)
> > > return;
> > >
> > > /*
> > > * Full dynticks uses IRQ work to drive the tick rescheduling on safe
> > > * locking contexts. But then we need IRQ work to raise its own
> > > * interrupts to avoid circular dependency on the tick.
> > > */
> > > if (!arch_irq_work_has_interrupt()) {
> > > pr_warn("NO_HZ: Can't run full dynticks because arch
> > > doesn't support IRQ work self-IPIs\n");
> > > cpumask_clear(tick_nohz_full_mask);
> > > tick_nohz_full_running = false;
> > > return;
> > > }
> > >
> > > Others LGTM!
> > >
> > > Reviewed-by: Guo Ren <guoren@...nel.org>
> > >
> > > > +}
> > > > +
> > > > +#endif /* _ASM_LOONGARCH_IRQ_WORK_H */
> > > > diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
> > > > index 278700cfee88..50db503f44e3 100644
> > > > --- a/arch/loongarch/include/asm/smp.h
> > > > +++ b/arch/loongarch/include/asm/smp.h
> > > > @@ -69,9 +69,11 @@ extern int __cpu_logical_map[NR_CPUS];
> > > > #define ACTION_BOOT_CPU 0
> > > > #define ACTION_RESCHEDULE 1
> > > > #define ACTION_CALL_FUNCTION 2
> > > > +#define ACTION_IRQ_WORK 3
> > > > #define SMP_BOOT_CPU BIT(ACTION_BOOT_CPU)
> > > > #define SMP_RESCHEDULE BIT(ACTION_RESCHEDULE)
> > > > #define SMP_CALL_FUNCTION BIT(ACTION_CALL_FUNCTION)
> > > > +#define SMP_IRQ_WORK BIT(ACTION_IRQ_WORK)
> > > >
> > > > struct secondary_data {
> > > > unsigned long stack;
> > > > diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> > > > index 1633ed4f692f..4272d2447445 100644
> > > > --- a/arch/loongarch/kernel/paravirt.c
> > > > +++ b/arch/loongarch/kernel/paravirt.c
> > > > @@ -2,6 +2,7 @@
> > > > #include <linux/export.h>
> > > > #include <linux/types.h>
> > > > #include <linux/interrupt.h>
> > > > +#include <linux/irq_work.h>
> > > > #include <linux/jump_label.h>
> > > > #include <linux/kvm_para.h>
> > > > #include <linux/static_call.h>
> > > > @@ -97,6 +98,11 @@ static irqreturn_t pv_ipi_interrupt(int irq, void *dev)
> > > > info->ipi_irqs[IPI_CALL_FUNCTION]++;
> > > > }
> > > >
> > > > + if (action & SMP_IRQ_WORK) {
> > > > + irq_work_run();
> > > > + info->ipi_irqs[IPI_IRQ_WORK]++;
> > > > + }
> > > > +
> > > > return IRQ_HANDLED;
> > > > }
> > > >
> > > > diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> > > > index 0dfe2388ef41..7366de776f6e 100644
> > > > --- a/arch/loongarch/kernel/smp.c
> > > > +++ b/arch/loongarch/kernel/smp.c
> > > > @@ -13,6 +13,7 @@
> > > > #include <linux/cpumask.h>
> > > > #include <linux/init.h>
> > > > #include <linux/interrupt.h>
> > > > +#include <linux/irq_work.h>
> > > > #include <linux/profile.h>
> > > > #include <linux/seq_file.h>
> > > > #include <linux/smp.h>
> > > > @@ -70,6 +71,7 @@ static DEFINE_PER_CPU(int, cpu_state);
> > > > static const char *ipi_types[NR_IPI] __tracepoint_string = {
> > > > [IPI_RESCHEDULE] = "Rescheduling interrupts",
> > > > [IPI_CALL_FUNCTION] = "Function call interrupts",
> > > > + [IPI_IRQ_WORK] = "IRQ work interrupts",
> > > > };
> > > >
> > > > void show_ipi_list(struct seq_file *p, int prec)
> > > > @@ -217,6 +219,13 @@ void arch_smp_send_reschedule(int cpu)
> > > > }
> > > > EXPORT_SYMBOL_GPL(arch_smp_send_reschedule);
> > > >
> > > > +#ifdef CONFIG_IRQ_WORK
> > > > +void arch_irq_work_raise(void)
> > > > +{
> > > > + mp_ops.send_ipi_single(smp_processor_id(), ACTION_IRQ_WORK);
> > > > +}
> > > > +#endif
> > > > +
> > > > static irqreturn_t loongson_ipi_interrupt(int irq, void *dev)
> > > > {
> > > > unsigned int action;
> > > > @@ -234,6 +243,11 @@ static irqreturn_t loongson_ipi_interrupt(int irq, void *dev)
> > > > per_cpu(irq_stat, cpu).ipi_irqs[IPI_CALL_FUNCTION]++;
> > > > }
> > > >
> > > > + if (action & SMP_IRQ_WORK) {
> > > > + irq_work_run();
> > > > + per_cpu(irq_stat, cpu).ipi_irqs[IPI_IRQ_WORK]++;
> > > > + }
> > > > +
> > > > return IRQ_HANDLED;
> > > > }
> > > >
> > > > --
> > > > 2.43.0
> > > >
> > >
> > >
> > > --
> > > Best Regards
> > > Guo Ren
>
>
>
> --
> Best Regards
> Guo Ren
>
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