linux-kernel - Re: Back to the future.

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Message-Id: <1177579723.5025.233.camel@nigel.suspend2.net>
Date:	Thu, 26 Apr 2007 19:28:43 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Back to the future.

Hi.

On Thu, 2007-04-26 at 11:17 +0300, Pekka Enberg wrote:
> Hi Nigel,
> 
> On 4/26/07, Nigel Cunningham <nigel@...el.suspend2.net> wrote:
> > * Doing things in the right order? (Prepare the image, then do the
> > atomic copy, then save).
> 
> As I am a total newbie to the power management code, I am unable to
> spot the conceptual difference in uswsusp suspend.c:suspend_system()
> and suspend2 kernel/power/suspend.c:suspend_main(). How are they
> different?

Will discuss in irc since you've appeared there...

> On 4/26/07, Nigel Cunningham <nigel@...el.suspend2.net> wrote:
> > * Mulithreaded I/O (might as well use multiple cores to compress the
> > image, now that we're hotplugging later).
> 
> I assume this doesn't affect the kernel at all with uswsusp?

Well uswsusp would benefit from using multiple threads - if it can - to
do the work. I saw quite an improvement from implementing it.

> On 4/26/07, Nigel Cunningham <nigel@...el.suspend2.net> wrote:
> > * Modular design?
> 
> This is too broad. Please be more specific of the problems the current
> suspend and snapshot/shutdown code in the kernel has.

Did you see the 'Reasons to merge' email I sent? It has more detail on
this.

> Now to add to your list, as far as I can tell, suspend2 provides
> better feedback to the user via the netlink mechanism (although the
> kernel shouldn't be sending messages such as userui_redraw but instead
> let the userspace know of the actual events, for example, that tasks
> have now been frozen). However, I am unsure if this is still relevant
> as most of the work (snapshot writing) is being done in userspace
> where we explicitly know when processes have been frozen, when the
> snapshot is finished, and when it's written to disk.

From uswsusp's point of view, yeah. But I'm still coming from the 'doing
this in kernelspace makes far more sense' perspective.

Regards,

Nigel

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