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

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Date:	Sun, 25 Oct 2015 07:58:42 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Florian Weimer <fweimer@...hat.com>
Cc:	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>,
	Peter Zijlstra <peterz@...radead.org>,
	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 11:47:04AM +0100, Florian Weimer wrote:
> On 10/25/2015 11:41 AM, Theodore Ts'o wrote:
> > On Sun, Oct 25, 2015 at 10:33:32AM +0100, Ingo Molnar wrote:
> >>
> >> Hm, that's weird - all our sched_*() system call APIs that set task scheduling 
> >> priorities are fundamentally per thread, not per process. Same goes for the old 
> >> sys_nice() interface. The scheduler has no real notion of 'process', and certainly 
> >> not at the system call level.
> >>
> > 
> > I suspect the main issue is that the games programmers were trying to
> > access it via libc / pthreads, which hides a lot of the power
> > available at the raw syscall level.  This is probably more of a
> > "tutorial needed for userspace programmers" issue, at a guess.
> 
> If this refers to the lack of exposure of thread IDs in glibc, we are
> willing to change that on glibc side.  The discussion has progressed to
> the point where it is now about the question whether it should be part
> of the GNU API (like sched_setaffinity), or live in glibc as a
> Linux-specific extension (like sched_getcpu).  More input is certainly
> welcome.

Well, I was thinking we could just teach them to use
"syscall(SYS_gettid)".

On a different subject, I'm going to start telling people to use
"syscall(SYS_getrandom)", since I think that's going to be easier than
having asking people to change their Makefiles to link against some
Linux-specific library, but that's a different debate, and I recognize
the glibc folks aren't willing to bend on that one.

Cheers,

					- Ted
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