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Subject: Re: [PATCH v5] x86/hpet: Reduce HPET counter read contention
To: Waiman Long <Waiman.Long@hpe.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
References: <1471037130-60583-1-git-send-email-Waiman.Long@hpe.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Borislav Petkov <bp@suse.de>,
        Andy Lutomirski <luto@kernel.org>, Prarit Bhargava <prarit@redhat.com>,
        Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>, Randy Wright <rwright@hpe.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <57AE41F3.6030107@intel.com>
Date: Fri, 12 Aug 2016 14:38:59 -0700
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On 08/12/2016 02:25 PM, Waiman Long wrote:
> + * The lock and the hpet value are stored together and can be read in a
> + * single atomic 64-bit read. It is explicitly assumed that the raw spinlock
> + * size is 32-bit.

So what happens when we have all the fun debugging options on?

> typedef struct raw_spinlock {
>         arch_spinlock_t raw_lock;
> #ifdef CONFIG_GENERIC_LOCKBREAK
>         unsigned int break_lock;
> #endif
> #ifdef CONFIG_DEBUG_SPINLOCK
>         unsigned int magic, owner_cpu;
>         void *owner;
> #endif
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
>         struct lockdep_map dep_map;
> #endif
> } raw_spinlock_t;