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

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Message-ID: <20191127173719.q3hrdthuvkt2h2ul@linutronix.de>
Date:   Wed, 27 Nov 2019 18:37:19 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH net 2/2] net: gro: Let the timeout timer expire in
 softirq context with `threadirqs'

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