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Message-ID: <Y4qX0uGWhqWO3vee@a4bf019067fa.jf.intel.com>
Date: Fri, 2 Dec 2022 16:26:58 -0800
From: Ashok Raj <ashok.raj@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>
CC: Borislav Petkov <bp@...en8.de>, X86-kernel <x86@...nel.org>,
"LKML Mailing List" <linux-kernel@...r.kernel.org>,
Dave Hansen <dave.hansen@...el.com>,
Tony Luck <tony.luck@...el.com>, <alison.schofield@...el.com>,
<reinette.chatre@...el.com>, Ashok Raj <ashok.raj@...el.com>
Subject: Re: [Patch V1 1/7] x86/microcode/intel: Remove redundant microcode
rev pr_info()s
On Fri, Dec 02, 2022 at 07:58:42PM +0100, Thomas Gleixner wrote:
> Ashok!
>
> On Tue, Nov 29 2022 at 13:08, Ashok Raj wrote:
> > There is a pr_info() to dump information about newly loaded microcode.
>
> There... Somewhere, right?
I'll make it clear, updated commit log below.
>
> > The code intends this pr_info() to be just once, but the check to ensure
> > is racy. Unfortunately this happens quite often in with this new change
> > resulting in multiple redundant prints on the console.
>
> -ENOPARSE. Can you try to express that in coherent sentences please?
:-)
>
> > microcode_init()->schedule_on_each_cpu(setup_online_cpu)->collect_cpu_info
> >
> > [ 33.688639] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
> > [ 33.688659] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
> > [ 33.688660] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
> >
> > There is already a pr_info() in microcode/core.c as shown below:
> >
> > microcode: Reload completed, microcode revision: 0x2b000041 -> 0x2b000070
>
> There are quite some pr_info()'s in microcode/core.c...
>
> $function_name() prints the new and the previous microcode revision once
> when the load has completed:
>
> microcode: Reload completed, microcode revision: 0x2b000041 -> 0x2b000070
>
> Hmm?
Agreed!
>
> > The sig and pf aren't that useful to end user, they are available via
>
> The sig and pf ?!? Come on, you really can do better.
>
> > /proc/cpuinfo and this never changes between microcode loads.
> >
> > Remove the redundant pr_info() and the racy single print checks. This
> > removes the race entirely, zap the duplicated pr_info() spam and
> > simplify the code.
>
> The last sentence does not qualify as coherent either.
>
> Other than that. Nice cleanup.
>
Thanks!. I'll try to get better at the commit log stuff
Updated commit log looks like below. Hope it doesn't get a -ENOPARSE this
time. :-)
------------------------
This code in collect_cpu_info() simply checks with a static variable "prev",
but when multiple CPUs are running this in parallel it is racy and we notice
the pr_info() couple times. The original intend was to print this just once.
New sequence shown below:
microcode_init()->schedule_on_each_cpu(setup_online_cpu)->collect_cpu_info
Resulting multiple prints below:
[ 33.688639] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
[ 33.688659] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
[ 33.688660] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
There is already a pr_info() in microcode_reload_late() that shows both the
old and new revisions as shown below.
microcode: Reload completed, microcode revision: 0x2b000041 -> 0x2b000070
The CPU signature (sig=0x50654) and Processor Flags (pf=0x80) above aren't
that useful to end user, they are available via /proc/cpuinfo and this never
changes between microcode loads.
Remove the redundant pr_info().
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