linux-kernel - Re: [patch 2/8] Implement always-locked bit ops, for memory shared with an SMP hypervisor.

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Date:	Thu, 3 Aug 2006 06:49:11 +0200
From:	Andi Kleen <ak@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	virtualization@...ts.osdl.org,
	Jeremy Fitzhardinge <jeremy@...p.org>, akpm@...l.org,
	xen-devel@...ts.xensource.com, Chris Wright <chrisw@...s-sol.org>,
	Ian Pratt <ian.pratt@...source.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/8] Implement always-locked bit ops, for memory shared with an SMP hypervisor.

On Thursday 03 August 2006 06:27, Christoph Lameter wrote:
> On Thu, 3 Aug 2006, Andi Kleen wrote:
> 
> > 
> > > Thats a good goal but what about the rest of us who have to maintain 
> > > additional forms of bit operations for all architectures. How much is this 
> > > burden?
> > 
> > I don't think it's that big an issue because most architectures either
> > use always locked bitops already or don't need them because they don't do
> > SMP.
> 
> Those architectures that always use locked bitops or dont need them would 
> not need to be modified if we put this in a special fail. I think this is 
> a i386 speciality here?

i386/x86-64

They could do a single line #include for asm-generic that defines them
to the normal bitops.


> 
> Those operations are only needed for special xen driver and not for 
> regular kernel code!

The Xen driver will be "regular" kernel code.

> > So it will be fine with just a asm-generic header that defines them
> > to the normal bitops. Not much burden.
> 
> asm-generic/xen-bitops.h asm-i386/xen-bitops.h is even less of a burden 
> and would only require a 
> 
> #include <asm/xen-bitops.h>
> 
> for those special xen drivers.

Well there might be reasons someone else uses this in the future too.
It's also not exactly Linux style - normally we try to add generic
facilities.

-Andi
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