linux-kernel - Re: [PATCH v5] x86/hpet: Reduce HPET counter read contention

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Date:	Fri, 12 Aug 2016 14:38:59 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Waiman Long <Waiman.Long@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Randy Wright <rwright@....com>
Subject: Re: [PATCH v5] x86/hpet: Reduce HPET counter read contention

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;