linux-kernel - Re: [PATCH 2/3] slub: Support for array operations

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, 11 Feb 2015 16:06:50 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
cc:	akpm@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, penberg@...nel.org, iamjoonsoo@....com
Subject: Re: [PATCH 2/3] slub: Support for array operations

On Thu, 12 Feb 2015, Jesper Dangaard Brouer wrote:

> > > This is quite an expensive lock with irqsave.
> >
> > Yes but we take it for all partial pages.
>
> Sure, that is good, but this might be a contention point. In a micro
> benchmark, this contention should be visible, but in real use-cases the
> given subsystem also need to spend time to use these elements before
> requesting a new batch (as long as NIC cleanup cycles don't get too
> synchronized)

Yes definitely it will be a contention point. There is no way around it.

> > Yup the page access is shared but there is one per page. Contention is
> > unlikely.
>
> Yes, contention is unlikely, but every atomic operation is expensive.
> On my system the measured cost is 8ns, and a lock/unlock does two, thus
> 16ns.  Which we then do per page freelist.

Not sure what we can do about this.

> > We can require that interrupt are off when the functions are called. Then
> > we can avoid the "save" part?
>
> Yes, we could also do so with an "_irqoff" variant of the func call,
> but given we are defining the API we can just require this from the
> start.

Allright. Lets do that then.
--
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/