linux-kernel - Re: [RFC 0/4] [RFC] slub: Fastpath optimization (especially for RT)

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: <alpine.DEB.2.11.1410230916090.19494@gentwo.org>
Date:	Thu, 23 Oct 2014 09:18:29 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	akpm@...uxfoundation.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-mm@...ck.org, penberg@...nel.org, iamjoonsoo@....com
Subject: Re: [RFC 0/4] [RFC] slub: Fastpath optimization (especially for
 RT)

On Thu, 23 Oct 2014, Joonsoo Kim wrote:

> Preemption disable during very short code would cause large problem for RT?

This is the hotpath and preempt enable/disable adds a significant number
of cycles.

> And, if page_address() and virt_to_head_page() remain as current patchset
> implementation, this would work worse than before.

Right.

> I looked at the patchset quickly and found another idea to remove
> preemption disable. How about just retrieving s->cpu_slab->tid first,
> before accessing s->cpu_slab, in slab_alloc() and slab_free()?
> Retrieved tid may ensure that we aren't migrated to other CPUs so that
> we can remove code for preemption disable.

You cannot do any of these things because you need the tid from the right
cpu and the scheduler can prempt you and reschedule you on another
processor at will. tid and c may be from different per cpu areas.
--
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/