linux-kernel - Re: [RFC PATCH 6/9] livepatch: create per-task consistency model

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Message-ID: <alpine.LNX.2.00.1502121340320.20672@pobox.suse.cz>
Date:	Thu, 12 Feb 2015 13:42:01 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>
Subject: Re: [RFC PATCH 6/9] livepatch: create per-task consistency model

On Thu, 12 Feb 2015, Peter Zijlstra wrote:

> > Well, the fact indisputable fact is that there is a demand for this. It's 
> > not about one machine, it's about scheduling dowtimes of datacentres.
> 
> The changelog says:
> 
>  > ... A patch can remain in the
>  > transition state indefinitely, if any of the tasks are stuck in the
>  > previous universe.
> 
> Therefore there is no scheduling anything. Without timeliness guarantees
> you can't make a schedule.
> 
> Might as well just reboot, at least that's fairly well guaranteed to
> happen.

All running (reasonably alive) tasks will be running patched code though. 

You can't just claim complete victory (and get ready for accepting another 
patch, etc) if there is a long-time sleeper that hasn't been converted 
yet.

-- 
Jiri Kosina
SUSE Labs
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