linux-kernel - Re: [PATCH RESEND] sched/nohz: Affine unpinned timers to housekeepers

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: <20150825082904.GA20562@gmail.com>
Date:	Tue, 25 Aug 2015 10:29:04 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Vatika Harlalka <vatikaharlalka@...il.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH RESEND] sched/nohz: Affine unpinned timers to housekeepers


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Mon, Aug 24, 2015 at 08:44:12AM +0200, Ingo Molnar wrote:
> > 2)
> > 
> > What happens if the boot CPU is offlined? (under CONFIG_BOOTPARAM_HOTPLUG_CPU0=y)
> > 
> > I don't see CPU hotplug callbacks fixing up the housekeeping_mask if the boot CPU 
> > is offlined.
> 
> We have tick_nohz_cpu_down_callback() which makes sure that the timekeeper, which
> is the boot CPU in nohz full, never gets offlined.

That solution really sucks - it essentially regresses a feature the user 
explicitly asked for! I also see no way for the user to migrate the timekeeping 
functionality over to another CPU without rebooting.

If this is the last timekeeping CPU then it should migrate the timekeeping 
functionality to another CPU, and perhaps printk a warning if all other CPUs are 
nohz-full and we have to mark one of them as the timekeeper.

Also, the nohz-full and timekeeper functionality should not be a boot parameter 
only thing, but should be runtime configurable.

Thanks,

	Ingo
--
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/