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From: Andrew Morton <akpm@linux-foundation.org>
To: "Christian Limpach" <Christian.Limpach@xensource.com>
Cc: "Jeremy Fitzhardinge" <jeremy@goop.org>,
	"Chris Wright" <chrisw@sous-sol.org>, "Andi Kleen" <ak@muc.de>,
	"Keir Fraser" <Keir.Fraser@cl.cam.ac.uk>,
	<xen-devel@lists.xensource.com>,
	"Ian Pratt" <Ian.Pratt@xensource.com>,
	<virtualization@lists.osdl.org>,
	"Steven Hand" <steven.hand@cl.cam.ac.uk>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [patch 14/21] Xen-paravirt: Add XEN config options and disableunsupported config options.
Date: Fri, 16 Feb 2007 02:09:47 -0800	[thread overview]
Message-ID: <20070216020947.03e1726e.akpm@linux-foundation.org> (raw)
In-Reply-To: <BBC437B5B077FF46935BA1D8C9A2172A01EBEBF4@exch2.ad.xensource.com>

On Fri, 16 Feb 2007 02:00:39 -0800 "Christian Limpach" <Christian.Limpach@xensource.com> wrote:

> Jeremy Fitzhardinge wrote:
> > Andrew Morton wrote:
> > > On Thu, 15 Feb 2007 22:14:45 -0800 Dan Hecht 
> > <dhecht@vmware.com> wrote:
> > >
> > >   
> > >>>  config PREEMPT
> > >>>  	bool "Preemptible Kernel (Low-Latency Desktop)"
> > >>> +	depends on !XEN
> > >>>  	help
> > >>>  	  This option reduces the latency of the kernel by making
> > >>>  	  all kernel code (that is not executing in a critical section)
> > >>>
> > >>>       
> > >
> > > Oh, so that's why it doesn't break when CONFIG_PREEMPT=y.  
> > In which case
> > > that preempt_disable() I spotted is wrong-and-unneeded.
> > >
> > > Why doesn't Xen work with preemption??
> > >   
> > 
> > I've forgotten the details.  Ian?  Keir?  Steven?  Maybe it 
> > can be done.
> 
> With CONFIG_PREEMPT, we can have preempted threads reference machine
> addresses across save/restore.  After restore, these machine addresses
> will be incorrect.
> 

It would help if you could define the terms "save/restore" and "machine
addresses".  One can guess, but there are probably subtleties here..

Are the places where the domU code references machine addresses splattered
all over the code?  If not, they can just be wrapped with
preempt_disable/preempt_enable?


WARNING: multiple messages have this Message-ID
From: Andrew Morton <akpm@linux-foundation.org>
To: Christian Limpach <Christian.Limpach@xensource.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
	Chris Wright <chrisw@sous-sol.org>, Andi Kleen <ak@muc.de>,
	Keir Fraser <Keir.Fraser@cl.cam.ac.uk>,
	xen-devel@lists.xensource.com,
	Ian Pratt <Ian.Pratt@xensource.com>,
	virtualization@lists.osdl.org,
	Steven Hand <steven.hand@cl.cam.ac.uk>,
	linux-kernel@vger.kernel.org
Subject: Re: [patch 14/21] Xen-paravirt: Add XEN config options and disableunsupported config options.
Date: Fri, 16 Feb 2007 02:09:47 -0800	[thread overview]
Message-ID: <20070216020947.03e1726e.akpm@linux-foundation.org> (raw)
In-Reply-To: <BBC437B5B077FF46935BA1D8C9A2172A01EBEBF4@exch2.ad.xensource.com>

On Fri, 16 Feb 2007 02:00:39 -0800 "Christian Limpach" <Christian.Limpach@xensource.com> wrote:

> Jeremy Fitzhardinge wrote:
> > Andrew Morton wrote:
> > > On Thu, 15 Feb 2007 22:14:45 -0800 Dan Hecht 
> > <dhecht@vmware.com> wrote:
> > >
> > >   
> > >>>  config PREEMPT
> > >>>  	bool "Preemptible Kernel (Low-Latency Desktop)"
> > >>> +	depends on !XEN
> > >>>  	help
> > >>>  	  This option reduces the latency of the kernel by making
> > >>>  	  all kernel code (that is not executing in a critical section)
> > >>>
> > >>>       
> > >
> > > Oh, so that's why it doesn't break when CONFIG_PREEMPT=y.  
> > In which case
> > > that preempt_disable() I spotted is wrong-and-unneeded.
> > >
> > > Why doesn't Xen work with preemption??
> > >   
> > 
> > I've forgotten the details.  Ian?  Keir?  Steven?  Maybe it 
> > can be done.
> 
> With CONFIG_PREEMPT, we can have preempted threads reference machine
> addresses across save/restore.  After restore, these machine addresses
> will be incorrect.
> 

It would help if you could define the terms "save/restore" and "machine
addresses".  One can guess, but there are probably subtleties here..

Are the places where the domU code references machine addresses splattered
all over the code?  If not, they can just be wrapped with
preempt_disable/preempt_enable?

  reply	other threads:[~2007-02-16 10:10 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-16 10:00 [patch 14/21] Xen-paravirt: Add XEN config options and disableunsupported config options Christian Limpach
2007-02-16 10:00 ` Christian Limpach
2007-02-16 10:09 ` Andrew Morton [this message]
2007-02-16 10:09   ` Andrew Morton
2007-02-16 10:47   ` Keir Fraser
2007-02-16 10:47   ` Keir Fraser
2007-02-16 10:47     ` Keir Fraser
2007-02-16 10:54     ` Andrew Morton
2007-02-16 10:54       ` Andrew Morton
2007-02-16 11:03       ` Keir Fraser
2007-02-16 11:03       ` Keir Fraser
2007-02-16 11:03         ` Keir Fraser
2007-02-16 17:46         ` [Xen-devel] " Jeremy Fitzhardinge
2007-02-16 17:46           ` Jeremy Fitzhardinge
2007-02-16 19:00           ` [Xen-devel] " Keir Fraser
2007-02-16 19:00           ` Keir Fraser
2007-02-16 19:00             ` Keir Fraser
2007-02-16 19:24             ` [Xen-devel] " Jeremy Fitzhardinge
2007-02-16 19:24               ` Jeremy Fitzhardinge
2007-02-16 21:51             ` [Xen-devel] " Zachary Amsden
2007-02-16 21:51               ` Zachary Amsden
2007-02-16 22:38               ` [Xen-devel] " Dan Hecht
2007-02-17 15:06                 ` Rik van Riel
2007-02-17 15:06                   ` Rik van Riel
2007-02-16 19:00           ` [Xen-devel] " Keir Fraser
2007-02-16 11:03       ` Keir Fraser
2007-02-16 10:47   ` Keir Fraser

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