linux-kernel - Re: [PATCH -v2 7/8] kexec jump: ftrace_enabled

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Message-ID: <20080811135136.GD28030@redhat.com>
Date:	Mon, 11 Aug 2008 09:51:36 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH -v2 7/8] kexec jump: ftrace_enabled_save/restore

On Mon, Aug 11, 2008 at 09:22:21AM +0800, Huang Ying wrote:
> Hi, Steven,
> 
> On Fri, 2008-08-08 at 10:30 -0400, Steven Rostedt wrote:
> [...]
> > The only problem with this approach is what happens if the user changes 
> > the enabled in between these two calls. This would make ftrace 
> > inconsistent.
> > 
> > I have a patch from the -rt tree that handles what you want. It is 
> > attached below. Not sure how well it will apply to mainline.
> > 
> > I really need to go through the rt patch set and start submitting a bunch 
> > of clean-up/fixes to mainline. We've been meaning to do it, just have been 
> > distracted :-(
> 
> Your version is better in general sense. Thank you very much!
> 
> But in this specific situation of kexec/kjump. The execution environment
> is that other CPUs are disabled, local irq is disabled, and it is not
> permitted to switch to other process. But it is safe and sufficient to
> use non-locked version here.
> 
> So to satisfy both demands, I think it is better to provide both
> version, locked and non-locked. What do you think about that?
> 

Huang,

So you want to use a non-locked version from optimization point of view?
So that we don't end up taking and release a lock?

Thanks
Vivek
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