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Subject: Re: [PATCH] nohz: Fix missing tick reprog while interrupting inline
 timer softirq
To:     Frederic Weisbecker <frederic@kernel.org>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Greg KH <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Anna-Maria Gleixner <anna-maria@linutronix.de>,
        <stable@vger.kernel.org>, Tero Kristo <t-kristo@ti.com>
References: <1533077570-9169-1-git-send-email-frederic@kernel.org>
 <8ecb9229-4c14-6967-0863-15b47cefd251@ti.com>
 <20180824061750.GA20523@kroah.com>
 <alpine.DEB.2.21.1808240851420.1668@nanos.tec.linutronix.de>
 <0d63c2bb-f75d-3f79-c19d-bb4ac9a00cd5@ti.com> <20180824184103.GD2730@lerouge>
From:   Grygorii Strashko <grygorii.strashko@ti.com>
Message-ID: <47d2416d-6359-1f48-311d-404fb5bfa3a8@ti.com>
Date:   Tue, 28 Aug 2018 12:56:53 -0500
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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