linux-kernel - Re: [RFC] [PATCH 0/2] x86: make jump labels use int3-based breakpoint instead of stop

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Date:	Wed, 10 Jul 2013 18:26:59 -0400
From:	Jason Baron <jbaron@...mai.com>
To:	Jiri Kosina <jkosina@...e.cz>
CC:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mathieu.desnoyers@...icios.com
Subject: Re: [RFC] [PATCH 0/2] x86: make jump labels use int3-based breakpoint
 instead of stop_machine()

On 07/10/2013 04:25 PM, Jiri Kosina wrote:
> Hi,
>
> this is a resurrection of a few years old idea to have jump labels use 
> synchronization based on int3 breakpoint rather than relying on 
> stop_machine() with all the consequences.
>
> ftrace has been doing exactly this kind of patching for year since 
> 08d636b6 ("ftrace/x86: Have arch x86_64 use breakpoints instead of stop 
> machine").
>
> This patchset first introduces generic text_poke_bp() that provides means 
> to perform this method of patching in parallel to text_poke_smp(), and 
> then converts x86 jump label code to use it.
>
> If this is merged, I'll do a followup patch converting ftrace to use this 
> infrastructure as well, as it's doing the same thing in principle already.
>
> Comments welcome.
>

Cool. This definitely an area I've wanted to improve with jump labels.

Perhaps, ftrace should be considered at this point to make sure the
interface is suitable for both callers?

Also, I wonder if its worth batching up updates. For example, right now
we simply update each call-site
one at a time even if its associated with the same control variable.

Thanks,

-Jason
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