linux-kernel - Re: [PATCH v6 3/4] perf,x86: add Intel RAPL PMU support

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:	Mon, 11 Nov 2013 17:16:31 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH v6 3/4] perf,x86: add Intel RAPL PMU support

On Mon, Nov 11, 2013 at 05:07:22PM +0100, Stephane Eranian wrote:
> On Mon, Nov 11, 2013 at 4:59 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Fri, Nov 08, 2013 at 08:46:02PM +0100, Stephane Eranian wrote:
> >
> >
> >> +static DEFINE_SPINLOCK(rapl_hotplug_lock);
> >
> > What is this thing protecting?
> >
> > Like last time it appears to be used only from hotplug notifier
> > callbacks and those are already fully serialized.
> >
> I thought you or somebody else had said, that hotplug in now parallel.

There's a little something about hotplug here I think:

 http://marc.info/?l=linux-kernel&m=138118235612441

But I'm not entirely sure that's the origin of this lock.

Andi seems worried about the IPI vs hotplug/migrate. I'm not entrely
sure the lock as proposed actually fixes that.

The 'easy' way would be to put a synchronize_sched() right after the
migrate code, that forces all CPUs to have scheduled once and thus also
ensures all pending/running interrupts are serviced.

But I don't think that's strictly required as I seem to recall hotplug
actually already does something like this -- it pretty much has to.
--
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/