linux-kernel - Re: [PATCH 10/10] softirq: Remove __ARCH_SET_SOFTIRQ

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Message-Id: <20180403075225.69ad3d25@mschwideX1>
Date:   Tue, 3 Apr 2018 07:52:25 +0200
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "James E . J . Bottomley" <jejb@...isc-linux.org>,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH 10/10] softirq: Remove __ARCH_SET_SOFTIRQ_PENDING

On Thu, 29 Mar 2018 20:08:36 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Mar 29, 2018 at 04:53:43PM +0200, Martin Schwidefsky wrote:
> > The lowcore optimization for softirq_pending field is not really needed,
> > just nice to have. But if there is a strong reason to make a common
> > definition for it we can certainly do that.  
> 
> A slightly related question; would it make sense to move all kernel
> static per-cpu stuff into lowcore, or is that asking for too much
> trickery?
 
The space in lowcore is quite limited, for zArch the structure is 8K with
many pre-defined fields. I fear that putting all of the static per-cpu
stuff in there is too much. 

So far I used the lowcore as optimization for selected per-cpu fields
which are performance relevant.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.