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From: zhukeqian <zhukeqian1@huawei.com>
To: <linux-arm-kernel@lists.infradead.org>,
	"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	"Suzuki K, Poulose" <suzuki.poulose@arm.com>
Cc: yebiaoxiang@huawei.com
Subject: [Question] About scaling factor of Enhanced Counter Virtualization
Date: Tue, 14 Jul 2020 10:20:07 +0800	[thread overview]
Message-ID: <e435efd2-f894-ecbb-5eb4-abf446aa1e56@huawei.com> (raw)

Hi all,

We are studying Enhanced Counter Virtualization (introduced by ARMv8.6 extension), and here is a question
raised by Biaoxiang Ye <yebiaoxiang@huawei.com>:

Described in the ARMv8.6 Extension Specification:
Note: the scaling factor CNTSCALE is designed as a 2.62 bit fixed point number, so permitting a scaling up by
(nearly) a factor 4. The scaling factor CNTISCALE is signed as an 8.56 number for the scaling of the values
written into the timers for comparison with the actual count. This implies that the greatest scaling down of the
counter supported in (nearly) a factor of *512*.

We think the number "512" should be "256" (2^8), or do we miss something?

Thanks,
Keqian
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             reply	other threads:[~2020-07-14  2:20 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-14  2:20 zhukeqian [this message]
2020-07-14 11:34 ` [Question] About scaling factor of Enhanced Counter Virtualization Marc Zyngier
2020-07-14 12:15   ` zhukeqian
2020-07-14 12:23     ` Marc Zyngier
2020-07-14 13:22       ` zhukeqian

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