netdev - Re: [PATCH net 2/2] net: gro: Let the timeout timer expire in softirq context with `threadirqs'

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Message-ID: <20200416135938.jiglv4ctjayg5qmg@linutronix.de>
Date:   Thu, 16 Apr 2020 15:59:38 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Eric Dumazet <edumazet@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net 2/2] net: gro: Let the timeout timer expire in
 softirq context with `threadirqs'

any comments from the timer department?

On 2019-11-27 18:37:19 [+0100], To Eric Dumazet wrote:
> On 2019-11-27 09:11:40 [-0800], Eric Dumazet wrote:
> > Resent in non HTML mode :/
> don't worry, mutt handles both :)
> 
> > Long story short, why hrtimer are not by default using threaded mode
> > in threadirqs mode ?
> 
> Because it is only documented to thread only interrupts. Not sure if we
> want change this.
> In RT we expire most of the hrtimers in softirq context for other
> reasons. A subset of them still expire in hardirq context.
>
> > Idea of having some (but not all of them) hard irq handlers' now being
> > run from BH mode,
> > is rather scary.
> 
> As I explained in my previous email: All IRQ-handlers fire in
> threaded-mode if enabled. Only the hrtimer is not affected by this
> change.
> 
> > Also, hrtimers got the SOFT thing only in 4.16, while the GRO patch
> > went in linux-3.19
> > 
> > What would be the plan for stable trees ?
> No idea yet. We could let __napi_schedule_irqoff() behave like
> __napi_schedule(). 

Sebastian