netdev - Re: [PATCH v2] nohz: prevent tilegx network driver interrupts

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Message-ID: <20150710224500.GA25028@jcartwri.amer.corp.natinst.com>
Date:	Fri, 10 Jul 2015 17:45:00 -0500
From:	Josh Cartwright <joshc@...com>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] nohz: prevent tilegx network driver interrupts

On Fri, Jul 10, 2015 at 03:37:25PM -0400, Chris Metcalf wrote:
> Normally the tilegx networking shim sends irqs to all the cores
> to distribute the load of processing incoming-packet interrupts,
> so that you can get to multiple Gb's of traffic inbound.
> 
> However, in nohz_full mode we don't want to interrupt the
> nohz_full cores by default, so we limit the set of cores we use
> to only the online housekeeping cores.
> 
> To make client code easier to read, we introduce a new nohz_full
> accessor, housekeeping_cpumask(), which returns a pointer to the
> housekeeping_mask if nohz_full is enabled, and otherwise returns
> the cpu_possible_mask.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
> ---
[..]
> +static inline const struct cpumask *housekeeping_cpumask(void)
> +{
> +#ifdef CONFIG_NO_HZ_FULL
> +	if (tick_nohz_full_enabled())
> +		return housekeeping_mask;
> +#endif

Just a small comment:

We can take these checks out from under a #ifdef CONFIG_NO_HZ_FULL
check, given that are stubbed tick_nohz_full_enabled() defined above.

  Josh

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