linux-kernel - Re: [PATCH] Convert powerpc simple spinlocks into ticket locks

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]

Message-ID: <1392001351.3996.16.camel@pasglop>
Date:	Mon, 10 Feb 2014 14:02:31 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Torsten Duwe <duwe@....de>
Cc:	Scott Wood <scottwood@...escale.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Tom Musta <tommusta@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks

On Fri, 2014-02-07 at 10:02 +0100, Torsten Duwe wrote:
> > > > Can you pair lwarx with sthcx ? I couldn't immediately find the answer
> > > > in the PowerISA doc. If so I think you can do better by being able to
> > > > atomically load both tickets but only storing the head without affecting
> > > > the tail.
> 
> Can I simply write the half word, without a reservation, or will the HW caches
> mess up the other half? Will it ruin the cache coherency on some (sub)architectures?

Yes, you can, I *think*

> > Plus, sthcx doesn't exist on all PPC chips.
> 
> Which ones are lacking it? Do all have at least a simple 16-bit store?

half word atomics (and byte atomics) are new, they've been added in architecture
2.06 I believe so it's fairly recent, but it's still worthwhile to investigate a
way to avoid atomics on unlock on recent processors (we can use instruction patching
if necessary based on CPU features) because there's definitely a significant cost
in doing a larx/stcx. sequence on powerpc, way higher than our current unlock path
of barrier + store.

Cheers,
Ben.


--
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/