Messages in this thread | | | Date | Wed, 29 Sep 2021 11:10:11 +0800 | From | Pingfan Liu <> | Subject | Re: [PATCHv2 4/5] irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64 |
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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?
[1]: https://lore.kernel.org/linux-arm-kernel/20201101131430.257038-1-maz@kernel.org/ [2]: https://lore.kernel.org/linux-arm-kernel/87lfewnmdz.fsf@nanos.tec.linutronix.de/
Thanks,
Pingfan
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