linux-kernel - RE: [PATCH v2 5/5] ARC: MCIP: Use IDU_M_DISTRI_DEST mode if there is only 1 destination core

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Message-ID: <3ABF60118B9B784CA5BF7C841D2F00EC0101864E@de02wembxa.internal.synopsys.com>
Date:   Tue, 25 Oct 2016 18:16:58 +0000
From:   Yuriy Kolerov <Yuriy.Kolerov@...opsys.com>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        Yuriy Kolerov <yuriy.kolerov@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "marc.zyngier@....com" <marc.zyngier@....com>,
        "Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: RE: [PATCH v2 5/5] ARC: MCIP: Use IDU_M_DISTRI_DEST mode if there
 is only 1 destination core

> -----Original Message-----
> From: Vineet Gupta [mailto:vgupta@...opsys.com]
> Sent: Tuesday, October 25, 2016 8:53 PM
> To: Yuriy Kolerov <yuriy.kolerov@...opsys.com>; linux-snps-
> arc@...ts.infradead.org
> Cc: marc.zyngier@....com; Vineet.Gupta1@...opsys.com;
> Alexey.Brodkin@...opsys.com; linux-kernel@...r.kernel.org;
> tglx@...utronix.de
> Subject: Re: [PATCH v2 5/5] ARC: MCIP: Use IDU_M_DISTRI_DEST mode if
> there is only 1 destination core
> 
> On 10/24/2016 05:46 AM, Yuriy Kolerov wrote:
> > ARC linux uses 2 distribution modes for common interrupts: round robin
> > mode (IDU_M_DISTRI_RR) and a simple destination mode
> (IDU_M_DISTRI_DEST).
> > The first one is used when more than 1 cores may handle a common
> > interrupt and the second one is used when only 1 core may handle a
> common interrupt.
> >
> > However idu_irq_set_affinity always sets IDU_M_DISTRI_RR for all
> > affinity values. But there is no sense in setting of such mode if only
> > 1 core must handle a common interrupt.
> >
> > Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
> > ---
> >  arch/arc/kernel/mcip.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c index
> > 090f0a1..75e6d73 100644
> > --- a/arch/arc/kernel/mcip.c
> > +++ b/arch/arc/kernel/mcip.c
> > @@ -197,6 +197,7 @@ idu_irq_set_affinity(struct irq_data *data, const
> > struct cpumask *cpumask,  {
> >  	unsigned long flags;
> >  	cpumask_t online;
> > +	unsigned long dest_bits;
> >
> >  	/* errout if no online cpu per @cpumask */
> >  	if (!cpumask_and(&online, cpumask, cpu_online_mask)) @@ -204,8
> > +205,14 @@ idu_irq_set_affinity(struct irq_data *data, const struct
> > cpumask *cpumask,
> >
> >  	raw_spin_lock_irqsave(&mcip_lock, flags);
> >
> > -	idu_set_dest(data->hwirq, cpumask_bits(&online)[0]);
> > -	idu_set_mode(data->hwirq, IDU_M_TRIG_LEVEL,
> IDU_M_DISTRI_RR);
> > +	dest_bits = cpumask_bits(&online)[0];
> > +	idu_set_dest(data->hwirq, dest_bits);
> > +
> > +	if (ffs(dest_bits) == fls(dest_bits)) {
> > +		idu_set_mode(data->hwirq, IDU_M_TRIG_LEVEL,
> IDU_M_DISTRI_DEST);
> > +	} else {
> > +		idu_set_mode(data->hwirq, IDU_M_TRIG_LEVEL,
> IDU_M_DISTRI_RR);
> > +	}
> 
> Better to use a local variable to assign IDU_M_xxx and then call
> idu_set_mode() outside the if. I know the compiler would do that anyways,
> but that looks simpler to read !

Yep.

> But on the other hand, adding all of this here - isn't there some sort of
> duplication of code now between here and in the idu_irq_xlate() ?
> Do we need the same stuff in 2 places ?

I tried to explain in in [PATCH v2 4/5]. In short I moved logic for setting affinity to idu_irq_set_affinity because xlate function is not the best place where it must be done (see commit message for that patch).

> >
> >  	raw_spin_unlock_irqrestore(&mcip_lock, flags);
> >
> >