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Date: Wed, 17 Nov 2010 00:52:55 -0800
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Jan Beulich <JBeulich@novell.com>
CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Eric Dumazet <dada1@cosmosbay.com>, xiyou.wangcong@gmail.com,
        Peter Zijlstra <peterz@infradead.org>, Nick Piggin <npiggin@kernel.dk>,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Xen-devel <xen-devel@lists.xensource.com>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        Avi Kivity <avi@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 09/14] xen/pvticketlock: Xen implementation for PV	 ticket
 locks
References: <cover.1289940821.git.jeremy.fitzhardinge@citrix.com><cover.1289940821.git.jeremy.fitzhardinge@citrix.com> <aa32da076143b8e13c23c1f589d7e6cbedb22907.1289940821.git.jeremy.fitzhardinge@citrix.com> <4CE39C3C0200007800022AE2@vpn.id2.novell.com>
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On 11/17/2010 12:11 AM, Jan Beulich wrote:
>>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@goop.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