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

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Date:	Sun, 25 Oct 2009 17:37:04 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
	Mike Travis <travis@....com>,
	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


* 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
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