linux-kernel - Re: [PATCH] nohz: Fix missing tick reprog while interrupting inline timer softirq

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Message-ID: <47d2416d-6359-1f48-311d-404fb5bfa3a8@ti.com>
Date:   Tue, 28 Aug 2018 12:56:53 -0500
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Frederic Weisbecker <frederic@...nel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        <stable@...r.kernel.org>, Tero Kristo <t-kristo@...com>
Subject: Re: [PATCH] nohz: Fix missing tick reprog while interrupting inline
 timer softirq



On 08/24/2018 01:41 PM, Frederic Weisbecker wrote:
> On Fri, Aug 24, 2018 at 11:10:44AM -0500, Grygorii Strashko wrote:
>> Yes. i do not see local_softirq_pending messages any more
>>
>> But one question, just to clarify, after patch "nohz: Fix missing tick reprog while interrupting inline timer softirq"
>> the tick_nohz_irq_exit() will be called few times in case of nested interrupts (min 2):
>> gic_handle_irq
>>   |- irq_exit
>>      |- preempt_count_sub(HARDIRQ_OFFSET);
>>      |-__do_softirq
>> 	<irqs enabled>
>> 	|- gic_handle_irq()
>> 	   |- irq_exit()
>> 		|- tick_irq_exit()
>> 		   if (!in_irq())
>> 			tick_nohz_irq_exit(); <-- [1]
>>      |- tick_irq_exit()
>> 	if (!in_irq())
>> 		tick_nohz_irq_exit(); <-- [2]
>>
>> Is it correct? in 4.14 tick_nohz_irq_exit() is much more complex then in LKML now,
>> and this is hot path.
> 
> That's correct and it's indeed more costly in 4.14 as then the tick is going to be programmed
> twice.
> 

Sry, that disturbing you all, but what are the conclusion here for 4.14.y?
- take Thomas's patch https://lore.kernel.org/patchwork/patch/969521/#1162900
- revert commit 2d898915ccf4838c04531c51a598469e921a5eb5


-- 
regards,
-grygorii