linux-kernel - Re: [GIT PULL] workqueue fixes for v4.3-rc5

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Date:	Mon, 19 Oct 2015 05:51:50 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Michal Hocko <mhocko@...e.cz>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Shaohua Li <shli@...com>, linux-mm <linux-mm@...ck.org>
Subject: Re: [GIT PULL] workqueue fixes for v4.3-rc5

On Wed, 2015-10-14 at 16:24 -0400, Tejun Heo wrote:

> But in terms of API consistency, it sucks to have queue_work()
> guarantee local queueing but not queue_delayed_work().  The ideal
> situation would be updating both so that neither guarantees.

You don't have to change anything to have neither guarantee local
queueing.  Called from a preemptible context, local means any CPU in
->cpus_allowed... which makes WORK_CPU_UNBOUND mean what one would
imagine WORK_CPU_UNBOUND to mean, not bound to any particular cpu.

      sh-16017   3.N.. 1510500545us : queue_work_on: golly, migrated cpu7 -> cpu3 -- target cpu8
      sh-16017   3.N.. 1510500550us : <stack trace>
 => tty_flip_buffer_push
 => pty_write
 => n_tty_write
 => tty_write
 => __vfs_write
 => vfs_write
 => SyS_write
 => entry_SYSCALL_64_fastpath

That was with a udelay(100) prior to disabling interrupts, but that just
makes it easier.

	-Mike

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