linux-kernel - Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread

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Message-ID: <20160229100110.GH6356@twins.programming.kicks-ass.net>
Date:	Mon, 29 Feb 2016 11:01:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	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>
Subject: Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of
 running thread

On Sat, Feb 27, 2016 at 10:35:28AM -0800, Linus Torvalds wrote:
> On Sat, Feb 27, 2016 at 6:58 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > Paul's patches have the following structure:
> >
> > struct thread_local_abi {
> >         union {
> >                 struct {
> >                         u32     cpu_id;
> >                         u32     seq;
> >                 };
> >                 u64 cpu_seq;
> >         };
> >         unsigned long post_commit_ip;
> > };
> 
> Please don't do "unsigned long" in ABI structures any more.
> 
> Make it u64, and make sure it is 64-bit aligned (which it would be in
> this case). Make it so that we don't have to have separate compat
> paths.

Yes, for sure. I was 'only' trying to reflect the state of the last rseq
patches. But yes, I should have called that out and avoided 'confusion'.