linux-kernel - Re: [RFC][PATCH 05/13] percpu-rwsem: Optimize readers and reduce global impact

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Message-ID: <20150629151220.GL15805@mtj.duckdns.org>
Date:	Mon, 29 Jun 2015 11:12:20 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Nicholas Mc Guire <der.herr@...r.at>, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, mingo@...hat.com,
	linux-kernel@...r.kernel.org, dave@...olabs.net, riel@...hat.com,
	viro@...IV.linux.org.uk, torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 05/13] percpu-rwsem: Optimize readers and reduce
 global impact

Hello, Peter.

On Mon, Jun 29, 2015 at 11:32:19AM +0200, Peter Zijlstra wrote:
> Agreed, luckily we already have the infrastructure for this, something
> like so?
> 
> --- a/include/linux/percpu-defs.h
> +++ b/include/linux/percpu-defs.h
> @@ -287,6 +287,16 @@ do {									\
>  	preempt_enable();						\
>  } while (0)
>  
> +#define per_cpu_sum(var)						\
> +({									\
> +	typeof(var) __sum = 0;						\
> +	int cpu;							\

Why not __cpu?

> +	compiletime_assert_atomic_type(__sum);				\
> +	for_each_possible_cpu(cpu)					\
> +		__sum += per_cpu(var, cpu);				\
> +	__sum;								\
> +})

But other than that, looks good to me.

Thanks.

-- 
tejun
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