Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757205AbYCTQRq (ORCPT ); Thu, 20 Mar 2008 12:17:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754318AbYCTQRh (ORCPT ); Thu, 20 Mar 2008 12:17:37 -0400 Received: from viefep18-int.chello.at ([213.46.255.22]:47564 "EHLO viefep16-int.chello.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754068AbYCTQRg (ORCPT ); Thu, 20 Mar 2008 12:17:36 -0400 X-SourceIP: 80.56.237.116 Subject: RE: [2.6.25-rc5-mm1][regression] ia64: hackbench doesn't finish>12 hour From: Peter Zijlstra To: "Luck, Tony" Cc: "Yu, Fenghua" , KOSAKI Motohiro , LKML , linux-ia64@vger.kernel.org, Hidetoshi Seto , Andrew Morton In-Reply-To: <1FE6DD409037234FAB833C420AA843ECDDA233@orsmsx424.amr.corp.intel.com> References: <20080318084314.FF0F.KOSAKI.MOTOHIRO@jp.fujitsu.com> <20080318094527.FF12.KOSAKI.MOTOHIRO@jp.fujitsu.com> <1205969039.6437.44.camel@lappy> <1FE6DD409037234FAB833C420AA843ECDDA233@orsmsx424.amr.corp.intel.com> Content-Type: text/plain Date: Thu, 20 Mar 2008 17:16:42 +0100 Message-Id: <1206029802.8514.406.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.21.92 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1377 Lines: 29 On Thu, 2008-03-20 at 09:04 -0700, Luck, Tony wrote: > > Which makes me wonder, why did you ever use a semaphore here? Looking at > > the code its a straight forward mutex. And when you would have used a > > mutex lockdep would have warned about this. > > The functionality that we are trying to add is to allow up to N > simultaneous processors to execute the critical region. On current > processors/platforms N=1 so a spinlock or mutex would be fine, but > there will be platforms for which N is a small integer greater than > one. Semaphore initialized to N looked to be the ideal primitive > for this (until Motohiro-san ran the test case that showed the path > where we call this code with a spinlock held). Right, no alternative there. > Next question is whether it is reasonable to get to this code > while holding a spinlock. Isn't this a problem for architectures > that need to use cross-processor interrupts to do a global TLB > shootdown? Yeah, semaphores can't be used from hardirq contexts for much the same reasons. But its all ia64 code, right? So I'm not directly seeing how other archs are affected here. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/