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Date: Mon, 27 Jun 2016 10:42:50 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, boqun.feng@gmail.com
Subject: Re: [PATCH 1/2] kernel/sched: introduce vcpu preempted interface
Message-ID: <20160627084250.GZ30154@twins.programming.kicks-ass.net>
References: <1466937715-6683-1-git-send-email-xinhui.pan@linux.vnet.ibm.com>
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On Sun, Jun 26, 2016 at 06:41:54AM -0400, Pan Xinhui wrote:

> +#ifdef arch_vcpu_is_preempted
> +static inline bool vcpu_is_preempted(int cpu)
> +{
> +	return arch_vcpu_is_preempted(cpu);
> +}
> +#else
> +static inline bool vcpu_is_preempted(int cpu)
> +{
> +	return 0;
> +}
> +#endif
> +
> +#ifdef arch_vcpu_get_yield_count
> +static inline unsigned int vcpu_get_yield_count(int cpu)
> +{
> +	return arch_vcpu_get_yield_count(cpu);
> +}
> +#else
> +static inline unsigned int vcpu_get_yield_count(int cpu)
> +{
> +	return 0;
> +}
> +#endif


Please, just do something like:

#ifndef vcpu_is_preempted
static inline bool vcpu_is_preempted(int cpu)
{
	return false;
}
#endif

No point in making it more complicated.

> +static inline bool
> +need_yield_to(int vcpu, unsigned int old_yield_count)

namespace... this thing should be called: vcpu_something()

> +{
> +	/* if we find the vcpu is preempted,
> +	* then we may want to kick it, IOW, yield to it
> +	*/
> +	return vcpu_is_preempted(vcpu) ||
> +		(vcpu_get_yield_count(vcpu) != old_yield_count);
> +}

And can you make doubly sure (and mention in the Changelog) that the OSQ
code compiles all this away when using these definitions.