netdev - Re: [PATCH 6/24] make atomic_read() behave consistently on frv

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:	Mon, 13 Aug 2007 02:44:13 -0400
From:	Chris Snook <csnook@...hat.com>
To:	David Howells <dhowells@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org, netdev@...r.kernel.org,
	akpm@...ux-foundation.org, ak@...e.de, heiko.carstens@...ibm.com,
	davem@...emloft.net, schwidefsky@...ibm.com, wensong@...ux-vs.org,
	horms@...ge.net.au, wjiang@...ilience.com, cfriesen@...tel.com,
	zlynx@....org, rpjday@...dspring.com, jesper.juhl@...il.com
Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv

David Howells wrote:
> Chris Snook <csnook@...hat.com> wrote:
> 
>> cpu_relax() contains a barrier, so it should do the right thing.  For non-smp
>> architectures, I'm concerned about interacting with interrupt handlers.  Some
>> drivers do use atomic_* operations.
> 
> I'm not sure that actually answers my question.  Why not smp_rmb()?
> 
> David

I would assume because we want to waste time efficiently even on non-smp 
architectures, rather than frying the CPU or draining the battery.  Certain 
looping execution patterns can cause the CPU to operate above thermal design 
power.  I have fans on my workstation that only ever come on when running 
LINPACK, and that's generally memory bandwidth-bound.  Just imagine what happens 
when you're executing the same few non-serializing instructions in a tight loop 
without ever stalling on memory fetches, or being scheduled out.

If there's another reason, I'd like to hear it too, because I'm just guessing here.

	-- Chris
-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html