linux-kernel - Re: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work

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:	Fri, 27 Mar 2015 13:02:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>, hannes@...xchg.org,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vinmenon@...eaurora.org, shashim@...eaurora.org,
	Michal Hocko <mhocko@...e.cz>, mgorman@...e.de,
	dave@...olabs.net, koct9i@...il.com,
	Linux Memory Management List <linux-mm@...ck.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work

On Fri, Mar 27, 2015 at 06:11:44AM -0500, Christoph Lameter wrote:
> On Fri, 27 Mar 2015, Peter Zijlstra wrote:
> 
> > > We could align the base on 8 bytes to gain an extra bit in the pointer
> > > and use that bit to indicate the running state. Then these sites can
> > > spin on that bit while we can change the actual base pointer.
> >
> > Even though tvec_base has ____cacheline_aligned stuck on, most are
> > allocated using kzalloc_node() which does not actually respect that but
> > already guarantees a minimum u64 alignment, so I think we can use that
> > third bit without too much magic.
> 
> Create a new slab cache for this purpose that does the proper aligning?

That is certainly a possibility, but we'll only ever allocate nr_cpus-1
entries from it, a whole new slab cache might be overkill.

What's not clear to me is why that thing is allocated at all, AFAICT
something like:

static DEFINE_PER_CPU(struct tvec_base, tvec_bases);

Should do the right thing and be much simpler.


--
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/