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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Jun 01, 2017 at 07:33:33PM +0200, Dario Faggioli wrote:
> Hello,
> 
> While chasing and dealing with bugs, over this last period, I've found myself
> augmenting Xen with quite a few new tracing capabilities, especially focusing
> on:
>  - IRQ being disabled and (re)enabled (in addition to the already existing
>    tracing of IRQ related activity that we have);
>  - RCU;
>  - softirqs (I think I sent a preliminary version of this, long ago, but can't
>    be sure);
>  - tasklets;
>  - timers;
> 
> And, apart from the first 4 patches (which are random, but still tracing
> related, of course, improvements), this is what this patch series does: it 
> adds
> tracing to the Xen susystems listed above.
> 
> That happens, one subsystem after another, in patches 6 to 15.
> 
> 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.

But perhaps that is more of an future idea as looking at the Linux code
it looks quite large and not that simple.

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