Messages in this thread Patch in this message | | | Date | Wed, 29 Sep 2021 22:29:09 +0800 | From | Pingfan Liu <> | Subject | Re: [PATCHv2 4/5] irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64 |
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On Wed, Sep 29, 2021 at 10:23:58AM +0100, Mark Rutland wrote: > On Wed, Sep 29, 2021 at 04:27:11PM +0800, Pingfan Liu wrote: > > On Wed, Sep 29, 2021 at 08:20:35AM +0100, Marc Zyngier wrote: > > > On Wed, 29 Sep 2021 04:10:11 +0100, > > > Pingfan Liu <piliu@redhat.com> wrote: > > > > > > > > On Tue, Sep 28, 2021 at 10:10:53AM +0100, Mark Rutland wrote: > > > > > On Fri, Sep 24, 2021 at 09:28:36PM +0800, Pingfan Liu wrote: > > > > > > The call to rcu_irq_enter() originated from gic_handle_irq() is > > > > > > redundant now, since arm64 has enter_from_kernel_mode() akin to > > > > > > irqenter_entry(), which has already called rcu_irq_enter(). > > > > > > > > > > Here I think you're referring to the call in handle_domain_irq(), but > > > > > that isn't clear from the commit message. > > > > > > > > > Yes, and I will make it clear in V2. > > > > > > > > > > Based on code analysis, the redundant can raise some mistake, e.g. > > > > > > rcu_data->dynticks_nmi_nesting inc 2, which causes > > > > > > rcu_is_cpu_rrupt_from_idle() unexpected. > > > > > > > > > > > > So eliminate the call to irq_enter() in handle_domain_irq(). And > > > > > > accordingly supplementing irq_enter_rcu(). > > > > > > > > > > We support many more irqchips on arm64, and GICv3 can be used on regular > > > > > 32-bit arm, so this isn't right. Moving the irq_enter_rcu() call > > > > > into the GICv3 driver specifically breaks other drivers on arm64 by > > > > > removing the call, and breaks the GICv3 driver on arm by adding a > > > > > duplicate call. > > > > > > > > > Oops. I forgot to protect the code in GICv3 with CONFIG_HAVE_ARCH_IRQENTRY > > > > > > > > > It looks like this should live in do_interrupt_handler() in > > > > > arch/arm64/kernel/entry-common.c, e.g. > > > > > > > > > > | static void do_interrupt_handler(struct pt_regs *regs, > > > > > | void (*handler)(struct pt_regs *)) > > > > > | { > > > > > | irq_enter_rcu(); > > > > > | if (on_thread_stack()) > > > > > | call_on_irq_stack(regs, handler); > > > > > | else > > > > > | handler(regs); > > > > > | irq_exit_rcu(); > > > > > | } > > > > > > > > > > ... unless there's some problem with that? > > > > > > > > > Yeah, do_interrupt_handler() is a more suitable place. But to resolve > > > > the performance regression of rescheduling IPI [1], it is badly demanded to > > > > distinguish irqnr before calling irq_enter_rcu() (please see 5/5 and [2] > > > > for the context). So it is a compromise to host the code in GICv3. > > > > > > > > Any good idea? > > > > > > There is no way we are going to single out a particular interrupt > > > controller. As for the "regression", we'll have to look at the numbers > > > once we have fixed the whole infrastructure. > > > > > But I just realize that at present, gic_handle_nmi() sits behind > > gic_handle_irq(). So it will make an mistaken for accounting of normal > > interrupt if calling irq_enter_rcu() in do_interrupt_handler(). > > We can restructure entry-common.c to avoid that if necessary. > > TBH, the more I see problems in this area the more I want to rip out the > pNMI bits... >
Overlook the undetermined pNMI, what about the partial patch like the following:
diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 32f9796c4ffe..3c46f8fd0e2e 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -219,17 +219,20 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs) lockdep_hardirqs_on(CALLER_ADDR0); } -static void noinstr enter_el1_irq_or_nmi(struct pt_regs *regs) +static bool noinstr enter_el1_irq_or_nmi(struct pt_regs *regs) { - if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs)) + if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs)) { arm64_enter_nmi(regs); - else + return false; + } else { enter_from_kernel_mode(regs); + return true; + } } -static void noinstr exit_el1_irq_or_nmi(struct pt_regs *regs) +static void noinstr exit_el1_irq_or_nmi(struct pt_regs *regs, bool is_irq) { - if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs)) + if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !is_irq) arm64_exit_nmi(regs); else exit_to_kernel_mode(regs); @@ -261,12 +264,19 @@ static void __sched arm64_preempt_schedule_irq(void) } static void do_interrupt_handler(struct pt_regs *regs, - void (*handler)(struct pt_regs *)) + void (*handler)(struct pt_regs *), + bool is_irq) { + if (likely(is_irq)) + irq_enter_rcu(); + if (on_thread_stack()) call_on_irq_stack(regs, handler); else handler(regs); + + if (likely(is_irq)) + irq_exit_rcu(); } extern void (*handle_arch_irq)(struct pt_regs *); @@ -435,10 +445,12 @@ asmlinkage void noinstr el1h_64_sync_handler(struct pt_regs *regs) static void noinstr el1_interrupt(struct pt_regs *regs, void (*handler)(struct pt_regs *)) { + bool is_irq; + write_sysreg(DAIF_PROCCTX_NOIRQ, daif); - enter_el1_irq_or_nmi(regs); - do_interrupt_handler(regs, handler); + is_irq = enter_el1_irq_or_nmi(regs); + do_interrupt_handler(regs, handler, is_irq); /* * Note: thread_info::preempt_count includes both thread_info::count @@ -449,7 +461,7 @@ static void noinstr el1_interrupt(struct pt_regs *regs, READ_ONCE(current_thread_info()->preempt_count) == 0) arm64_preempt_schedule_irq(); - exit_el1_irq_or_nmi(regs); + exit_el1_irq_or_nmi(regs, is_irq); } asmlinkage void noinstr el1h_64_irq_handler(struct pt_regs *regs) -- 2.31.1
And the rest of do_interrupt_handler() in entry-common.c should be converted accordingly.
Thanks,
Pingfan
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