From: Marc Zyngier <maz@kernel.org>
To: zhukeqian <zhukeqian1@huawei.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
yebiaoxiang@huawei.com, Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [Question] About scaling factor of Enhanced Counter Virtualization
Date: Tue, 14 Jul 2020 13:23:12 +0100 [thread overview]
Message-ID: <eda57587fe701c9eee8641c94496dbc3@kernel.org> (raw)
In-Reply-To: <0bbe0709-c055-2d97-9a88-814821dd9c2f@huawei.com>
On 2020-07-14 13:15, zhukeqian wrote:
> Hi Marc,
>
> On 2020/7/14 19:34, Marc Zyngier wrote:
>> Hi Keqian,
>>
>> On 2020-07-14 03:20, zhukeqian wrote:
>>> 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?
>>
>> This register doesn't seem to be described in ARM DDI 0487F.b,
>> which is the official documentation and does contain the ARMv8.6
>> material, including ARMv8.6-ECV.
>>
>> Either you are looking at confidential information (and nobody
>> can answer you in public), or obsolete information (and nobody
>> knows what this is about).
>>
> Well, it's alpha release version :( . Many thanks!
Wow. I suggest you discard this document, as it is obsolete.
ARMv8.6 is a released version of the architecture, and
everything should be in the ARM ARM.
M.
--
Jazz is not dead. It just smells funny...
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next prev parent reply other threads:[~2020-07-14 12:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-14 2:20 [Question] About scaling factor of Enhanced Counter Virtualization zhukeqian
2020-07-14 11:34 ` Marc Zyngier
2020-07-14 12:15 ` zhukeqian
2020-07-14 12:23 ` Marc Zyngier [this message]
2020-07-14 13:22 ` zhukeqian
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