linux-kernel - Re: [v2] powerpc: handle simultaneous interrupts at once

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Message-ID: <1496661424.31588.1.camel@kernel.crashing.org>
Date:   Mon, 05 Jun 2017 21:17:04 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Michael Ellerman <patch-notifications@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Paul Mackerras <paulus@...ba.org>,
        Scott Wood <oss@...error.net>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [v2] powerpc: handle simultaneous interrupts at once

On Mon, 2017-06-05 at 20:21 +1000, Michael Ellerman wrote:
> On Thu, 2017-03-16 at 08:55:45 UTC, Christophe Leroy wrote:
> > It often happens to have simultaneous interrupts, for instance
> > when having double Ethernet attachment. With the current
> > implementation, we suffer the cost of kernel entry/exit for each
> > interrupt.
> > 
> > This patch introduces a loop in __do_irq() to handle all interrupts
> > at once before returning.
> > 
> > Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> 
> Applied to powerpc next, thanks.
> 
> https://git.kernel.org/powerpc/c/45cb08f4791ce6a15c54598b4cb73d

Hrm, I hadn't noticed that patch...

We used to do that and then removed the code for it. There's a cost,
sometimes noticeable, to an extra call to ppc_md.get_irq.

Why not have your get_irq (or eoi) implementation set a per-cpu
requesting a new spin of the loop ?

We could move the xive force replay stuff to use the same thing.

Ben.