linux-kernel - Re: [PATCH 6/8] SGI x86_64 UV: Limit the number of microcode messages

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Message-ID: <b647ffbd0910261311n4ac4471el7a32ac41104cf93b@mail.gmail.com>
Date:	Mon, 26 Oct 2009 21:11:54 +0100
From:	Dmitry Adamushko <dmitry.adamushko@...il.com>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Andreas Mohr <andi@...as.de>, Hugh Dickins <hugh@...itas.com>,
	Hannes Eder <hannes@...neseder.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] SGI x86_64 UV: Limit the number of microcode messages

2009/10/26 Mike Travis <travis@....com>:
>
>
> Ingo Molnar wrote:
>>
>> * Dmitry Adamushko <dmitry.adamushko@...il.com> wrote:
>>
>>> 2009/10/24 Tigran Aivazian <tigran@...azian.fsnet.co.uk>:
>>>>
>>>> On Sat, 24 Oct 2009, Dmitry Adamushko wrote:
>>>>>>
>>>>>> -       printk(KERN_INFO "microcode: CPU%d sig=0x%x, pf=0x%x,
>>>>>> revision=0x%x\n",
>>>>>> +       if (cpu_num < 4 || !limit_console_output(false))
>>>>>> +               printk(KERN_INFO
>>>>>> +                       "microcode: CPU%d sig=0x%x, pf=0x%x,
>>>>>> revision=0x%x\n",
>>>>>>                       cpu_num, csig->sig, csig->pf, csig->rev);
>>>>>>
>>>>> Hmm, I guess we wouldn't lose a lot by simply removing those messages
>>>>> completely. Per-cpu pf/revision is available via /sys anyway.
>>>>
>>>> The reason for printing them is that the pf (possibly others?) can
>>>> change by the update and so the log has this info handy.
>>>
>>> We might store the old sig/pf/revision set as well, export them via
>>> /sys or/and print them at update-to-new-microcode time.
>>>
>>> If it's really so useful to have this info in the log and, at the same
>>> time, to avoid the flood of messages (which, I guess for the majority
>>> of systems, are the same) at startup time, we might delay the printout
>>> until the end of microcode_init(). Then do something like this:
>>>
>>> microcode cpu0: up to date version sig, pf, rev          // let's say,
>>> it was updated by BIOS
>>> microcode cpus [1 ... 16] : update from sig, pf, rev to sig, pf2, rev2.
>>>
>>> Anyway, my humble opinion, is that (at the very least) the current
>>> patch should be accompanied by a similar version for amd.
>>
>> yeah. Since we load new microcode on all cpus it's enough to print it for
>> the boot CPU or so.
>>
>> Having the precise microcode version printed (or exposed somewhere in
>> /sys) is useful - sometimes when there's a weird crash in some prototype CPU
>> one of the first questions from hw vendors is 'which precise microcode
>> version was that?'.
>>
>>        Ingo
>
> I would agree especially in the case where not all the cpus are exactly
> the same.  But so far, I've only seen variations of the speed of the cpus
> not it's generic type, in an SSI.  So the version of the microcode was
> identical in all cases.

I guess that (at least) a bootup cpu can be updated by BIOS so that it
may appear to be different.
Perhaps, cases where some 'broken' cpus have been replaced for others
with a different "revision" (but still compatible otherwise) might be
rare but possible (say, big machines with hot-pluggable cpus) ?

btw., I was thinking of having something like this:

microcode: cpus [K...L]  platform-specific-format (e.g. for Intel :
sig, pf, rev)
microcode: updating...
microcode: cpus [K...L]  platform-specific-format (e.g. for Intel :
sig, pf, rev)

or even just,

microcode: cpus [ K...L] updated from platform-specific-format-1 to
platform-specific-format-2


>
> Thanks,
> Mike
>


-- Dmitry
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