netdev - Re: [PATCH 3/3] Convert the UDP hash lock to RCU

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: <20081007143346.GA6384@linux.vnet.ibm.com>
Date:	Tue, 7 Oct 2008 07:33:46 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Corey Minyard <minyard@....org>,
	David Miller <davem@...emloft.net>, dada1@...mosbay.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	shemminger@...tta.com
Subject: Re: [PATCH 3/3] Convert the UDP hash lock to RCU

On Tue, Oct 07, 2008 at 09:16:13AM -0500, Christoph Lameter wrote:
> Evgeniy Polyakov wrote:
> > On Mon, Oct 06, 2008 at 06:08:09PM -0500, Corey Minyard (minyard@....org) wrote:
> >> Would using SLAB_DESTROY_BY_RCU be ok, or would that be too expensive?
> > 
> > I tested skb destruction via RCU path, and got 2.5 times worse numbers
> > with small-packets-bulk-transfer workload.
> 
> Was this with regular RCU freeing? This will cool down the cacheline before
> frees. You need SLAB_DESTROY_BY_RCU to keep the objects cache hot.

Indeed!

But care is required -- SLAB_DESTROY_BY_RCU permits objects to be freed
and reallocated while a reader holds a reference.  The only guarantee is
that the -type- of the data structure will not change while a reader holds
a reference.  With something like UDP, this might well be sufficient.

Just be careful!  ;-)

							Thanx, Paul
--
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