linux-kernel - Re: [PATCH 1/2] Make the batch size of the percpu

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: <1367348457.27102.197.camel@schen9-DESK>
Date:	Tue, 30 Apr 2013 12:00:57 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] Make the batch size of the percpu_counter
 configurable

On Tue, 2013-04-30 at 18:27 +0000, Christoph Lameter wrote:
> On Tue, 30 Apr 2013, Tim Chen wrote:
> 
> > > But you will have to dereference the pointer whenever you want the batch
> > > size from the hot path. Looks like it would be better to put the value
> > > there directly. You have a list of percpu counters that can be traversed
> > > to change the batch size.
> > >
> >
> > I have considered that.  But the list is not available unless we have
> > CONFIG_HOTPLUG_CPU compiled in.
> 
> percpu counters are performance sensitive and with the pointer you
> will need to reference another one increasing the cache footprint. You are
> touching an additional cacheline somewhere in memory frequently. Not good.
> 

Seems like there's objection to make batch a pointer and I'll have to
store its value in per cpu pointer.

Will it be acceptable if I make the per cpu counter list under
CONFIG_CPU_HOTPLUG default? I will need the list to go through all
counters to update the batch value sizes.  The alternative will be to
make the configurable batch option only available under
CONFIG_HOTPLUG_CPU.

Which is the preferable approach or there are other clever alternatives?

Tim

--
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/