linux-kernel - Re: [patch 9/9] Scheduler profiling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 31 May 2007 18:07:42 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 9/9] Scheduler profiling - Use conditional calls

* Andi Kleen (andi@...stfloor.org) wrote:
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> writes:
> >  	}
> > -	profile_hit(SCHED_PROFILING, __builtin_return_address(0));
> > +	cond_call(profile_on,
> > +		profile_hit(SCHED_PROFILING, __builtin_return_address(0)));
> 
> Would it be possible to use a syntax like
> 
>         if (unlikely_cond_call(variable)) {     (or better name) 
>                 ...
>         } 
> 
> instead? I think that would be much nicer to read than having
> code in a macro argument
> 

I see your point, but there is a level of control on the branch I would
lack by doing so: the ability to put the call in either the if or else
branch. It is an optimization on i386.

I could do it by defining my home-made if() :

cond_if (cond_call_name) {
  code
}

The macro cond_if could then expand (this is a simplified example) in either in

if (cond)

or

if (cond)
else

Also, I live in the expectation that, someday, the gcc guys will be nice
enough to add some kind of support for a nop-based jump that would
require code patching to put a jump instead. If it ever happens, my
macro could evolve into this for newer compiler versions, which I could
not do with the if() statement you are proposing.


-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/