linux-kernel - Re: [PATCH] x86/smp: Fix __max_logical

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Message-ID: <20160811134651.GW30192@twins.programming.kicks-ass.net>
Date:	Thu, 11 Aug 2016 15:46:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Frank Ramsay <framsay@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH] x86/smp: Fix __max_logical_packages value setup

On Thu, Aug 11, 2016 at 03:05:21PM +0200, Jiri Olsa wrote:
> hum, so we either need some acpi solution to get number of all
> sockets or

This.. So the problem here is that the BIOS completely screws us over.

It wrecks the ACPI-ID table with that option to limit the number of CPUs
exposed to the OS (note that it didn't need to do that, it could have
enumerated them as empty, instead of not there at all) while keeping the
CPUID of the CPUs as reporting they have many (12? was it) cores.

This results in inconsistent state, and we're left with nothing useful.

> fix the uncore code to initialize pmu boxes on cpu hotplug as well

Can't.. it uses the boxes at STARTING time, and we can't do allocs
there. Not can we alloc earlier, because we don't know max_packages is
going to increase.