linux-kernel - Re: [PATCH] x86/MCE: Remove MCP

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Date:   Tue, 8 Nov 2016 22:14:04 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
cc:     "Luck, Tony" <tony.luck@...el.com>,
        linux-edac <linux-edac@...r.kernel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/MCE: Remove MCP_TIMESTAMP

On Tue, 8 Nov 2016, Borislav Petkov wrote:
> On Tue, Nov 08, 2016 at 09:39:02PM +0100, Thomas Gleixner wrote:
> > That does not make any sense. Where is m.tsc initialized? I couldn't find
> > any place which does, except this and the conditional clear farther down in
> > that function.
> 
> mce_gather_info->mce_setup does
> 
> m->tsc = rdtsc();
> 
> And we do that *everytime* but then we go and clear the damn thing. I
> know, I know, I wanted to flip that logic too and read the TSC *only*
> when we want a precise timestamp but that would require more changes as
> mce_setup() is used at a bunch of places.

And yes, you should spend the extra cycles. Adding a flags argument to
mce_setup() and propagate it through the various callsites shouldn't be
that hard and would make the stuff obvious instead of obfuscated.

Thanks,

	tglx