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 for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Mon, 2 Nov 2015 16:06:46 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 3/4] x86,asm: Re-work smp_store_mb()

On Mon, Nov 2, 2015 at 12:15 PM, Davidlohr Bueso <dave@...olabs.net> wrote:
>
> So I ran some experiments on an IvyBridge (2.8GHz) and the cost of XCHG is
> constantly cheaper (by at least half the latency) than MFENCE. While there
> was a decent amount of variation, this difference remained rather constant.

Mind testing "lock addq $0,0(%rsp)" instead of mfence? That's what we
use on old cpu's without one (ie 32-bit).

I'm not actually convinced that mfence is necessarily a good idea. I
could easily see it being microcode, for example.

At least on my Haswell, the "lock addq" is pretty much exactly half
the cost of "mfence".

                     Linus
--
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/

Powered by blists - more mailing lists