Re: [Xen-devel] [PATCHv4 5/8] xen: use ticket locks for spin locks

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-04-30 at 16:33 +0100, David Vrabel wrote:
>  
>  void _spin_lock_irq(spinlock_t *lock)
>  {
> -    LOCK_PROFILE_VAR;
> -
>      ASSERT(local_irq_is_enabled());
>      local_irq_disable();
> -    check_lock(&lock->debug);
> -    while ( unlikely(!_raw_spin_trylock(&lock->raw)) )
> -    {
> -        LOCK_PROFILE_BLOCK;
> -        local_irq_enable();
> -        while ( likely(_raw_spin_is_locked(&lock->raw)) )
> -            cpu_relax();
> -        local_irq_disable();
> -    }
> -    LOCK_PROFILE_GOT;
> -    preempt_disable();
> +    _spin_lock(lock);

This (and the irqsave variant) differs in that it spins/waits with irq's
disabled unlike the previous implementation which enabled irqs while it
waited.

Is this change intentional? I think it warrants a mention and rationale
in the commit log if so.



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