linux-kernel - Re: [PATCH] Fix WARN_ON / WARN_ON

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]

Message-Id: <1159918976.8035.59.camel@localhost.localdomain>
Date:	Tue, 03 Oct 2006 16:42:56 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	herbert@...dor.apana.org.au, linux-kernel@...r.kernel.org,
	leonid.i.ananiev@...el.com
Subject: Re: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

On Tue, 2006-10-03 at 17:07 -0700, Andrew Morton wrote:

> > 
> > introduced 40% more 2nd level cache miss to tbench workload
> > being run in a loop back mode on a Core 2 machine.  I think the
> > introduction of the local variables to WARN_ON and WARN_ON_ONCE
> > 
> > typeof(x) __ret_warn_on = (x);
> > typeof(condition) __ret_warn_once = (condition);
> > 
> > results in the extra cache misses.
> 
> I don't see why it should.
> 

Before the WARN_ON/WARN_ON_ONCE patch, the condition given to
WARN_ON/WARN_ON_ONCE is evaluated once and that's it.  But after the
patch, the condition is stored in a variable and returned later.  I
think that accessing this variable causes cache misses.

> Perhaps the `static int __warn_once' is getting put in the same cacheline
> as some frequently-modified thing.   Perhaps try marking that as __read_mostly?
> 

I'll give that a try to see if it will improve things.

Tim
-
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/