linux-kernel - Re: [PATCH 0/2] jump label: 2.6.38 updates

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: <1297718964.23343.75.camel@gandalf.stny.rr.com>
Date:	Mon, 14 Feb 2011 16:29:24 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Will Newton <will.newton@...il.com>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	hpa@...or.com, mingo@...e.hu, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	masami.hiramatsu.pt@...achi.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, sam@...nborg.org,
	ddaney@...iumnetworks.com, michael@...erman.id.au,
	linux-kernel@...r.kernel.org, Mike Frysinger <vapier@...too.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	dhowells <dhowells@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"heiko.carstens" <heiko.carstens@...ibm.com>,
	benh <benh@...nel.crashing.org>
Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates

On Mon, 2011-02-14 at 19:24 +0100, Peter Zijlstra wrote:
> On Mon, 2011-02-14 at 17:50 +0000, Will Newton wrote:
> > 
> > It would observe a stale value, but that value would only be updated
> > when the cache line was reloaded from main memory which would have to
> > be triggered by either eviction or cache flushing. So it could get
> > pretty stale. Whilst that's probably within the spec. of atomic_read I
> > suspect it would lead to problems in practice. I could be wrong
> > though. 
> 
> Right, so the typical scenario that could cause pain is something like:
> 
> while (atomic_read(&foo) != n)
>   cpu_relax();
> 
> and the problem is that cpu_relax() doesn't know which particular
> cacheline to flush in order to make things go faster, hm?

But what about any global variable? Can't we also just have:

	while (global != n)
		cpu_relax();

?

-- Steve


--
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/