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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 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... > Could you give further comments and some guide to my reply to [1/5], which can help to decide pNMI at this earlier stage? If things can go that way, then everything can be fixed easier. I think they abstract the ability of irqchip by exporting two interfaces: void (*handle_arch_nmi)(struct pt_regs *regs); bool (*interrupt_is_nmi)(void); And each irqchip can select whether to implement or not. > > And going through drivers/irqchip/irq-chip-gic*, I think there are only > > two files should be handled: irq-gic.c and irq-gic-v3.c. > > That are irqchips other than GICv2 and GICv3 that are used as the root > irqchip on arm64. For example, Raspberry Pi 3 uses > drivers/irqchip/irq-bcm2836.c as its root irqchip. > Thanks for the explanation. The situation is worse than I had thought. And no way out in that direction. Thanks, Pingfan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel