From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: linux-next: build failure after merge of the tip tree Date: Mon, 20 Jan 2014 01:23:00 -0800 Message-ID: <52DCEAF4.3040902@zytor.com> References: <20140116145829.5e4fcab103b1c5c77501ee77@canb.auug.org.au> <20140116121955.GQ31570@twins.programming.kicks-ass.net> <20140117074628.88698f59939c9002b7c12968@canb.auug.org.au> <20140120082620.GB30183@twins.programming.kicks-ass.net> <52DCE4CF.2060605@zytor.com> <20140120091600.GW31570@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from terminus.zytor.com ([198.137.202.10]:42057 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753068AbaATJXp (ORCPT ); Mon, 20 Jan 2014 04:23:45 -0500 In-Reply-To: <20140120091600.GW31570@twins.programming.kicks-ass.net> Sender: linux-next-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Len Brown , Stephen Rothwell , Thomas Gleixner , Ingo Molnar , linux-next@vger.kernel.org, "linux-kernel@vger.kernel.org" On 01/20/2014 01:16 AM, Peter Zijlstra wrote: >> >> The difference is the STI! > > So do the local_irq_enable(); mwait_idle_with_hints(0,0); thing. > No, that doesn't work. The point of __sti_mwait() is that the STI is the instruction immediately before the MWAIT, just like the combination STI;HLT. Since the execution of STI is always delayed by one instruction, these two instructions form an atomic unit, which means interrupts are enabled "after" we have entered MWAIT or HLT. > But that's entirely different from saying that core2 doesn't support > mwait_idle_with_hints because its a different instruction. If you think of STI;MWAIT as a "compound instruction" it kind of is. Newer CPUs don't have to play that trick anymore, because there is a flag to MWAIT which breaks us out of MWAIT on a pending interrupt without having to actually enable interrupts at the point of the MWAIT. -hpa