Re: [PATCH 00/15] xen/tools: add tracing to various Xen subsystems

From: Dario Faggioli <dario.faggioli@citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	Jennifer Herbert <jennifer.herbert@citrix.com>,
	xen-devel@lists.xenproject.org,
	Doug Goldstein <cardoe@cardoe.com>
Subject: Re: [PATCH 00/15] xen/tools: add tracing to various Xen subsystems
Date: Thu, 8 Jun 2017 18:45:57 +0200	[thread overview]
Message-ID: <1496940357.26212.2.camel@citrix.com> (raw)
In-Reply-To: <20170607141343.GB32578@char.us.oracle.com>

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On Wed, 2017-06-07 at 10:13 -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, Jun 01, 2017 at 07:33:33PM +0200, Dario Faggioli wrote:
> > 
> > Patch 5 deserves special mention. In fact, now that we have
> > Kconfig, I thought
> > it could be a nice thing to make it possible to select, at build
> > config time,
> > whether we want tracing or not, in the hypervisor (like, for
> > instance, we do
> > for performance counters).
> 
> Did you have thoughts on perhaps using asm goto as an
> alterantive to unlikely?
> 
> In Linux it is called jump labels or such - the idea is that the 
> code has (by default and on x86) five NOP instructions. But you
> can patch it over and add an call to the unlikely code.
> 
Yes, I know. I've never actually looked at the code, but I know they do
that, and I think it's cool.

> But perhaps that is more of an future idea as looking at the Linux
> code
> it looks quite large and not that simple.
> 
I would love for us to do something similar in Xen. I've _thought_
about that many times, but that's it. :-/

Let's see... right now, I can't look into this, as I agree with you
that it would be a major piece of work.

But yes, it's been in my thoughts! :-)

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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