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

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  Re: [PATCH v2] nohz: prevent tilegx network driver interrupts Josh Cartwright <joshc@ni.com> - 2015-07-11 00:50 +0200
    Re: [PATCH v2] nohz: prevent tilegx network driver interrupts Chris Metcalf <cmetcalf@ezchip.com> - 2015-07-11 01:10 +0200
      Re: [PATCH v2] nohz: prevent tilegx network driver interrupts Josh Cartwright <joshc@ni.com> - 2015-07-11 01:20 +0200

#1181980 — Re: [PATCH v2] nohz: prevent tilegx network driver interrupts

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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@ezchip.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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#1181985

On 7/10/2015 6:45 PM, Josh Cartwright wrote:
>> +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.

True for the "if" clause, but the "housekeeping_mask" variable is only defined
under CONFIG_NO_HZ_FULL.

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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#1181995

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On Fri, Jul 10, 2015 at 07:06:23PM -0400, Chris Metcalf wrote:
> On 7/10/2015 6:45 PM, Josh Cartwright wrote:
> >>+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.
> 
> True for the "if" clause, but the "housekeeping_mask" variable is only defined
> under CONFIG_NO_HZ_FULL.

Indeed!  I should have read more carefully.

Sorry for the noise.

  Josh

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