linux-kernel - Re: [PATCH 3/3] sched: Implement interface for cgroup unified hierarchy

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Date:	Mon, 26 Oct 2015 15:10:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Florian Weimer <fweimer@...hat.com>
Cc:	Theodore Ts'o <tytso@....edu>, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Li Zefan <lizefan@...wei.com>,
	cgroups <cgroups@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-team <kernel-team@...com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] sched: Implement interface for cgroup unified
 hierarchy

On Sun, Oct 25, 2015 at 02:17:23PM +0100, Florian Weimer wrote:
> On 10/25/2015 12:58 PM, Theodore Ts'o wrote:
> 
> > Well, I was thinking we could just teach them to use
> > "syscall(SYS_gettid)".
> 
> Right, and that's easier if TIDs are officially part of the GNU API.
> 
> I think the worry is that some future system might have TIDs which do
> not share the PID space, or are real descriptors (that they need
> explicit open and close operations).

For the scheduler the sharing of pid/tid space is not an issue.

Semantically all [1] scheduler syscalls take a tid. There isn't a single
syscall that iterates the thread group.

Even sys_setpriority() interprets its @who argument as a tid when
@which == PRIO_PROCESS (PRIO_PGRP looks to be the actual process).

[1] as seen from: git grep SYSCALL kernel/sched/


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