linux-kernel - Re: [PATCH v13 00/12] support "task

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Date:	Sun, 17 Jul 2016 19:42:50 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Chris Metcalf <cmetcalf@...lanox.com>,
	Gilad Ben Yossef <giladb@...lanox.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 00/12] support "task_isolation" mode

On Thu, 14 Jul 2016, Andy Lutomirski wrote:

> As an example, enough vmalloc/vfree activity will eventually cause
> flush_tlb_kernel_range to be called and *boom*, there goes your shiny
> production dataplane application.  Once virtually mapped kernel stacks
> happen, the frequency with which this happens will only increase.

But then vmalloc/vfre activity is not to be expected if user space only is
running. Since the kernel is not active and this affects kernel address
space only it could be deferred. Such events will cause OS activity that
causes a number of high latency events but then the system will quiet down
again.

> On very brief inspection, __kmem_cache_shutdown will be a problem on
> some workloads as well.

These are all corner cases that can be worked on over time if they are
significant. The main issue here is to reduce the obvious and relatively
frequent causes for ticks and allow easier detection of events that cause
tick activity.