linux-kernel - Re: [PATCH 09/14] xen/pvticketlock: Xen implementation for PV ticket locks

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Date:	Wed, 17 Nov 2010 00:52:55 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Eric Dumazet <dada1@...mosbay.com>, xiyou.wangcong@...il.com,
	Peter Zijlstra <peterz@...radead.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Avi Kivity <avi@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 09/14] xen/pvticketlock: Xen implementation for PV	 ticket
 locks

On 11/17/2010 12:11 AM, Jan Beulich wrote:
>>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>> +static void xen_lock_spinning(struct arch_spinlock *lock, unsigned want)
>>  {
>> -	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
>> -	struct xen_spinlock *prev;
>>  	int irq = __get_cpu_var(lock_kicker_irq);
>> -	int ret;
>> +	struct xen_lock_waiting *w = &__get_cpu_var(lock_waiting);
>> +	int cpu = smp_processor_id();
>>  	u64 start;
>>  
>>  	/* If kicker interrupts not initialized yet, just spin */
>>  	if (irq == -1)
>> -		return 0;
>> +		return;
>>  
>>  	start = spin_time_start();
>>  
>> -	/* announce we're spinning */
>> -	prev = spinning_lock(xl);
>> +	w->want = want;
>> +	w->lock = lock;
>> +
>> +	/* This uses set_bit, which atomic and therefore a barrier */
>> +	cpumask_set_cpu(cpu, &waiting_cpus);
> Since you don't allow nesting, don't you need to disable
> interrupts before you touch per-CPU state?

Yes, I think you're right - interrupts need to be disabled for the bulk
of this function.

    J
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