linux-kernel - Re: [RFC PATCH v6 1/5] Thread-local ABI system call: cache CPU number of running thread

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Message-ID: <57068FCC.8000701@redhat.com>
Date:	Thu, 7 Apr 2016 18:50:20 +0200
From:	Florian Weimer <fweimer@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-api <linux-api@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Watson <davejwatson@...com>, Chris Lameter <cl@...ux.com>,
	Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: Re: [RFC PATCH v6 1/5] Thread-local ABI system call: cache CPU number
 of running thread

On 04/07/2016 06:39 PM, Linus Torvalds wrote:

> Can anybody give a *coherent* and actual *real* reason why the kernel
> would ever care about anything else?

We already have a similar per-thread data structure, the robust mutex
list.  The CPU ID is another one.  So it's conceivable we might get
further such fields in the future.

(AFAICS set_robust_list was designed with such extensions in mind.)

Florian