linux-kernel - Re: [PATCH -tip -v6] irq_work: generic hard-irq context callbacks

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Date:	Wed, 29 Sep 2010 16:29:52 +0800
From:	huang ying <huang.ying.caritas@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Huang Ying <ying.huang@...el.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	paulus <paulus@...ba.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	dhowells <dhowells@...hat.com>,
	Russell King <rmk@....linux.org.uk>,
	Kyle McMartin <kyle@...artin.ca>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	davem <davem@...emloft.net>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH -tip -v6] irq_work: generic hard-irq context callbacks

Hi, Frederic,

On Tue, Sep 28, 2010 at 11:56 PM, Frederic Weisbecker
<fweisbec@...il.com> wrote:
> On Tue, Sep 28, 2010 at 04:51:48PM +0800, Huang Ying wrote:
>> +++ b/arch/x86/kernel/irq_work.c
>> @@ -0,0 +1,30 @@
>> +/*
>> + * x86 specific code for irq_work
>> + *
>> + * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@...hat.com>
>> + */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/irq_work.h>
>> +#include <linux/hardirq.h>
>> +#include <asm/apic.h>
>> +
>> +void smp_irq_work_interrupt(struct pt_regs *regs)
>> +{
>> +     irq_enter();
>> +     ack_APIC_irq();
>> +     inc_irq_stat(apic_irq_work_irqs);
>> +     irq_work_run();
>> +     irq_exit();
>> +}
>> +
>> +void arch_irq_work_raise(void)
>> +{
>> +#ifdef CONFIG_X86_LOCAL_APIC
>> +     if (!cpu_has_apic)
>> +             return;
>> +
>> +     apic->send_IPI_self(IRQ_WORK_VECTOR);
>> +     apic_wait_icr_idle();
>> +#endif
>> +}
>
>
>
> So basically, CONFIG_X86_LOCAL_APIC == !HAVE_IRQ_WORK ?
>
> But IIUC, this will fallback to the timer interrupt:

If !CONFIG_X86_LOCAL_APIC or !cpu_has_apic, this will fallback to the
timer interrupt.

>> @@ -1279,7 +1279,10 @@ void update_process_times(int user_tick)
>>       run_local_timers();
>>       rcu_check_callbacks(cpu, user_tick);
>>       printk_tick();
>> -     perf_event_do_pending();
>> +#ifdef CONFIG_IRQ_WORK
>> +     if (in_irq())
>> +             irq_work_run();
>> +#endif
>>       scheduler_tick();
>>       run_posix_cpu_timers(p);
>>  }
>
> Then HAVE_IRQ_WORK just means that the arch supports self IPIs.

HAVE_IRQ_WORK means IRQ_WORK is supported on the architecture, it has
nothing to do with self IPIs.

Best Regards,
Huang Ying
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