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Date:   Tue, 3 Apr 2018 10:42:01 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc:     Frederic Weisbecker <frederic@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Tony Luck <tony.luck@intel.com>,
        "David S . Miller" <davem@davemloft.net>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Helge Deller <deller@gmx.de>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        "James E . J . Bottomley" <jejb@parisc-linux.org>,
        heiko.carstens@de.ibm.com
Subject: Re: [PATCH 10/10] softirq: Remove __ARCH_SET_SOFTIRQ_PENDING
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On Tue, Apr 03, 2018 at 07:52:25AM +0200, Martin Schwidefsky wrote:
> On Thu, 29 Mar 2018 20:08:36 +0200
> Peter Zijlstra <peterz@infradead.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.

Fair enough; and yes 8k isn't much. Thanks for the info.