linux-kernel - Re: [thisops uV3 15/18] Xen: Use this_cpu

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Date:	Tue, 30 Nov 2010 12:53:55 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Christoph Lameter <cl@...ux.com>
CC:	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org
Subject: Re: [thisops uV3 15/18] Xen: Use this_cpu_ops

On 11/30/2010 11:07 AM, Christoph Lameter wrote:
>  static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
>  {
> -	struct clock_event_device *evt = &__get_cpu_var(xen_clock_events);
>  	irqreturn_t ret;
>  
>  	ret = IRQ_NONE;
> -	if (evt->event_handler) {
> -		evt->event_handler(evt);
> +	if (__this_cpu_read(xen_clock_events.event_handler)) {
> +		__this_cpu_read(xen_clock_events.event_handler)(evt);

Really?  What code does this generate?  If this is generating two
segment-prefixed reads rather than getting the address and doing normal
reads on it, then I don't think it is an improvement.

The rest looks OK, I guess.  How does it change the generated code?

    J
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