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Subject: Re: [PATCH v6] 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: <1471049968-63172-1-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>
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Date: Thu, 25 Aug 2016 11:50:14 -0700
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On 08/12/2016 05:59 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 arch_spinlock_t
> + * is 32 bits in size.

This requirement forces us to give up all of the goodness of lockdep.
Is this strictly a performance optimization or is there some function
requirement behind it as well?