linux-kernel - Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

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Date:	Thu, 13 Mar 2014 12:01:58 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Stefani Seibold <stefani@...bold.net>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	andriy.shevchenko@...ux.intel.com,
	Martin Runge <Martin.Runge@...de-schwarz.com>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

On 03/13/2014 11:32 AM, Andy Lutomirski wrote:
> 
> I don't recall anyone suggesting keeping the name.  CONFIG_COMPAT_VDSO
> will henceforth be a silly name, since the "compat" mode won't have a
> vdso.
> 

Linus suggested it:
> What might be acceptable then is to just keep the old config name, and
> if the COMPAT_VDSO config is enabled, you just disable the non-compat
> vdso. At least that way, presumably any opensuse people would have
> their kernel config continue working.

	...

> The consensus was that the default should be no vdso, right?  My most
> recent patchset calls it CONFIG_ENABLE_VDSO32_BY_DEFAULT and defaults
> to n.

On any practical system, the vdso needs to be turned on -- the syscall
performance difference is very significant.

>> It is important that anyone who actually cares about performance unsets
>> the option.
> 
> Should there be a warning at startup if the option is set?

Possibly.  Not sure if anyone will read it.

	-hpa


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