linux-kernel - Re: [PATCH] genirq: reduce irqdebug bouncing cachelines

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Message-ID: <8f7b2768-fe69-b1eb-8fc0-dc77a394ae99@kaod.org>
Date:   Wed, 14 Apr 2021 15:13:14 +0200
From:   Cédric Le Goater <clg@...d.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] genirq: reduce irqdebug bouncing cachelines

On 4/13/21 10:24 PM, Thomas Gleixner wrote:
> 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?

It does not add much benefits on the 2s and 4s systems but I will give it 
a try on bigger ones when I can grab them. Then we can decide if it is 
worth merging. 

Thanks,

C.