linux-kernel - Re: [PATCH 4/6] x86-mce: Add spinlocks to prevent duplicated MCP and CMCI reports.

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Date:	Fri, 18 Jul 2014 14:23:04 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Havard Skinnemoen <hskinnemoen@...gle.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ewout van Bekkum <ewout@...gle.com>
Subject: Re: [PATCH 4/6] x86-mce: Add spinlocks to prevent duplicated MCP and
 CMCI reports.

On Thu, Jul 17, 2014 at 3:50 AM, Borislav Petkov <bp@...en8.de> wrote:
> Well, maybe it is about time we tracked shared banks.

For cpus that support CMCI and the MCi_CTL2 registers we do track
sharing. Only one cpu gets to be the "owner" of a bank that supports
CMCI (the first one to find it and set bit 30 in the CTL2 register).

The test_bit()  at the top of the loop in machine_check_poll() makes
sure only the owner of a bank actually looks at it.

        for (i = 0; i < mca_cfg.banks; i++) {
                if (!mce_banks[i].ctl || !test_bit(i, *b))
                        continue;

If we don't have CMCI, then we don't have the CTL2 registers, and
so have no way to find out which banks are shared.

> We can evaluate later if the IRQs disabling is too heavy after all.

I'd be surprised if it was a problem in practice. If we have  CMCI,
then we limit the banks that we look at (and if we see a high rate
of interrupts, then we turn off interrupts an poll).

If we don't have CMCI, then we are polling at a pretty low rate
(current code adjusts the rate higher if we are finding errors to
log, but we don't let that rate rise forever ... cap is ~ 1HZ).

-Tony
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