linux-kernel - Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz

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.2.11.1510122151460.6097@nanos>
Date:	Mon, 12 Oct 2015 21:52:08 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Dave Jones <davej@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is
 set"

On Mon, 12 Oct 2015, Frederic Weisbecker wrote:
> This reverts commit 8cb9764fc88b41db11f251e8b2a0d006578b7eb4.
> 
> We assumed that nohz full users always want scheduler isolation on full
> dynticks CPUs, therefore we included nohz full CPUs on cpu_isolated_map.
> This means that tasks run by default on CPUs outside the nohz_full range
> unless their affinity is explicity overwritten.
> 
> This suits pure isolation workloads but when the machine is needed to
> run common workloads, the available sets of CPUs to run common tasks
> becomes reduced.
> 
> We reach an extreme case when CONFIG_NO_HZ_FULL_ALL is enabled as it
> leaves only CPU 0 for non-isolation tasks, which makes people think that
> their supercomputer regressed to 90's UP.
> 
> Some nohz full users appear to be interested in running normal workloads
> either before or after an isolation workload. Nohz full isn't optimized
> toward normal workloads but it's still better than UP performance.
> 
> We are reaching a limitation in kernel presets here. Lets revert this
> cpu_isolated_map inclusion and let userspace do its own scheduler
> isolation using cpusets or explicit affinity settings.

Acked-by: Thomas Gleixner <tglx@...utronix.de>
--
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/