linux-kernel - Re: [PATCH] Skip tsc synchronization checks if CONSTANT

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Message-ID: <20081024192532.GG27492@one.firstfloor.org>
Date:	Fri, 24 Oct 2008 21:25:32 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>, akataria@...are.com,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Daniel Hecht <dhecht@...are.com>
Subject: Re: [PATCH] Skip tsc synchronization checks if CONSTANT_TSC bit is set.

> BIOSes are also just software, and we have to deal with bugs in them 
> *all the time*.  The reality is that we're going to have to deal with 
> both vendor and user reluctance to upgrade, and therefore have to deal 
> with brokenness in the field. 

In the field they will just continue using clock=pit, like they
always did on vmware. And also they will not update the Linux kernel.

This is strictly for new installations. And I frankly don't 
see why Linux needs to get white listed workarounds when the 
Hypervisor couldn't as well be fixed. We have the bizarre
situation here where a HV vendor tries to add workarounds
to Linux instead of fixing it on their products.

Now making generic code a little more flexible in what
it accepts is fine though (like relaxing tsc_sync or 
checking and trusting UNSTABLE_TSC). That will scale at least
and doesn't need significant new code.

-Andi

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