Re: [PATCH] genirq: reduce irqdebug bouncing cachelines

From: Thomas Gleixner <tglx@linutronix.de>
To: "Cédric Le Goater" <clg@kaod.org>, "Nicholas Piggin" <npiggin@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] genirq: reduce irqdebug bouncing cachelines
Date: Tue, 13 Apr 2021 22:24:28 +0200	[thread overview]
Message-ID: <87tuoax79f.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <b299bb0c-2997-6f6f-8646-4a7ecb2c79c0@kaod.org>

On Tue, Apr 13 2021 at 14:16, Cédric Le Goater wrote:
>>> We could test irq_settings_no_debug() directly under handle_nested_irq() 
>>> and handle_irq_event_percpu() to avoid calling note_interrupt(), just 
>>> like we do for noirqdebug.
>> 
>> We can do that, but then we should not just make it:
>> 
>>    if (!irqnodebug && !irq_settings_no_debug(desc))
>>    	note_interrupt(...);
>> 
>> Instead have only one condition:
>> 
>>    if (!irq_settings_no_debug(desc))
>>    	note_interrupt(...);
>> 
>> See the uncompiled delta patch below.
>
> I merged this second part with the first and gave IRQF_NO_DEBUG a try 
> on P8 and P9 systems and all looked fine. I should send both patches 
> after IRQF_NO_AUTOEN is merged in mainline.     

Does having that NODEBUG flag set on the IPI irqs make a measurable
difference or is it just too small to matter?

Thanks,

        tglx