linux-kernel - RE: [PATCH v4] trace,x86: add x86 irq vector tracepoints

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Date:	Thu, 11 Oct 2012 17:04:03 +0000
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	"Thomas Gleixner (tglx@...utronix.de)" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"'mingo@...e.hu' (mingo@...e.hu)" <mingo@...e.hu>,
	"x86@...nel.org" <x86@...nel.org>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [PATCH v4] trace,x86: add x86 irq vector tracepoints

> >
> > I didn't say anything magic, but a table of pointers that are very
> > critical for the system running. Should we implement it with a single
> > switch, like we discussed in San Diego to do with the system call table?
> >
> > That is, have a "normal" table, and a "trace" table. The trace table
> > points to functions that have tracepoints. The first enabler of
> > tracing switches the table to use the tracepoints, and the last
> > disabler switches it back?
> >
> 
> That is certainly a reasonable implementation option.  It is slightly less usable than it is for system calls, though, because the vectors in
> the IDTs are somewhat scrambled and so you can't just do an indirect jump to the original vector content.  This does get messy
> because you also want to preserve registers...
> 

Peter, Steven, 

Thank you for explaining the reason why you think a time penalty should be zero
and discussing its implementation.

I will update my patch so that a time penalty makes zero and submit it shortly.

Seiji
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