linux-kernel - Re: [PATCH] arm64: restore bogomips information in /proc/cpuinfo

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Date:	Wed, 25 Nov 2015 09:32:14 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Jon Masters <jcm@...masters.org>
CC:	Will.Deacon@....com, Catalin.Marinas@....com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH] arm64: restore bogomips information in /proc/cpuinfo

On 11/25/2015 7:16 AM, Nicolas Pitre wrote:
> On Wed, 25 Nov 2015, Jon Masters wrote:
>
>> On 11/18/15, 1:15 PM, Yang Shi wrote:
>>
>>> As what Pavel Machek reported [1], some userspace applications depend on
>>> bogomips showed by /proc/cpuinfo.
>>>
>>> Although there is much less legacy impact on aarch64 than arm, but it does
>>> break libvirt.
>>>
>>> Basically, this patch reverts commit
>>> 326b16db9f69fd0d279be873c6c00f88c0a4aad5
>>> ("arm64: delay: don't bother reporting bogomips in /proc/cpuinfo"), but with
>>> some tweak due to context change.
>>
>> On a total tangent, it would be ideal to (eventually) have something reported
>> in /proc/cpuinfo or dmesg during boot that does "accurately" map back to the
>> underlying core frequency (as opposed to the generic timer frequency). I have
>> seen almost countless silly situations in the industry (external to my own
>> organization) in which someone has taken a $VENDOR_X reference system that
>> they're not supposed to run benchmarks on, and they've done it anyway. But
>> usually on some silicon that's clocked multiples under what production would
>> be. Then silly rumors about performance get around because nobody can do
>> simple arithmetic and notice that they ought to have at least divided by some
>> factor.
>
> Be my guest my friend.
>
> According to the common wisdom, the bogomips reporting is completely
> senseless at this point and no one should expect anything useful from
> it. Therefore I attempted to rehabilitate some meaning into it given
> that we just can't get rid of it either and it continues to cause
> dammage. You certainly saw where that has led me.

Or we may create a new one, i.e. "cpu MHz" like x86? Then we keep both 
in cpuinfo so that the userspace could adopt it gradually?

Thanks,
Yang

>
>
> Nicolas
>

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