netdev - Re: [PATCH] percpu: add optimized generic percpu accessors

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:	Wed, 21 Jan 2009 23:45:01 +1100
From:	Stephen Hemminger <shemminger@...tta.com>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	akpm@...ux-foundation.org, hpa@...or.com, brgerst@...il.com,
	cl@...ux-foundation.org, travis@....com,
	linux-kernel@...r.kernel.org, steiner@....com, hugh@...itas.com,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors

On Wed, 21 Jan 2009 03:21:23 -0800
ebiederm@...ssion.com (Eric W. Biederman) wrote:

> Tejun Heo <tj@...nel.org> writes:
> 
> > Ingo Molnar wrote:
> >> The larger point still remains: the kernel dominantly uses static percpu 
> >> variables by a margin of 10 to 1, so we cannot just brush away the static 
> >> percpu variables and must concentrate on optimizing that side with 
> >> priority. It's nice if the dynamic percpu-alloc side improves as well, of 
> >> course.
> >
> > Well, the infrequent usage of dynamic percpu allocation is in some
> > part due to the poor implementation, so it's sort of chicken and egg
> > problem.  I got into this percpu thing because I wanted a percpu
> > reference count which can be dynamically allocated and it sucked.
> 
> Counters are our other special case, and counters are interesting
> because they are individually very small.  I just looked and the vast
> majority of the alloc_percpu users are counters.
> 
> I just did a rough count in include/linux/snmp.h  and I came
> up with 171*2 counters.  At 8 bytes per counter that is roughly
> 2.7K.  Or about two thirds of a 4K page.

This is crap. only a small fraction of these SNMP counters are
close enough to the hot path to deserve per-cpu treatment.
--
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