Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753333AbbHCLvW (ORCPT ); Mon, 3 Aug 2015 07:51:22 -0400 Received: from smtprelay2.synopsys.com ([198.182.60.111]:57467 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752832AbbHCLvU convert rfc822-to-8bit (ORCPT ); Mon, 3 Aug 2015 07:51:20 -0400 From: Vineet Gupta To: Peter Zijlstra CC: lkml , "arc-linux-dev@synopsys.com" Subject: Re: [PATCH 4/6] ARC: LLOCK/SCOND based rwlock Thread-Topic: [PATCH 4/6] ARC: LLOCK/SCOND based rwlock Thread-Index: AQHQzeBAC2yV2Imr+UmjXO5stlww0Q== Date: Mon, 3 Aug 2015 11:51:15 +0000 Message-ID: References: <1438596188-10875-1-git-send-email-vgupta@synopsys.com> <1438596188-10875-5-git-send-email-vgupta@synopsys.com> <20150803113331.GJ25159@twins.programming.kicks-ass.net> Accept-Language: en-US, en-IN Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.12.197.191] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1343 Lines: 42 On Monday 03 August 2015 05:03 PM, Peter Zijlstra wrote: > On Mon, Aug 03, 2015 at 03:33:06PM +0530, Vineet Gupta wrote: >> With LLOCK/SCOND, the rwlock counter can be atomically updated w/o need >> for a guarding spin lock. > Maybe re-iterate the exclusive vs shared spin story again. > > And aside from the far too many full barriers (again), I was just > wondering about: > >> +static inline void arch_write_unlock(arch_rwlock_t *rw) >> +{ >> + unsigned int val; >> + >> + smp_mb(); >> + >> + /* >> + * rw->counter = __ARCH_RW_LOCK_UNLOCKED__; >> + */ >> + __asm__ __volatile__( >> + "1: llock %[val], [%[rwlock]] \n" >> + " scond %[UNLOCKED], [%[rwlock]]\n" >> + " bnz 1b \n" >> + " \n" >> + : [val] "=&r" (val) >> + : [rwlock] "r" (&(rw->counter)), >> + [UNLOCKED] "r" (__ARCH_RW_LOCK_UNLOCKED__) >> + : "memory", "cc"); >> + >> + smp_mb(); >> +} > Why can't that be a straight store? Right - that was my overly cautious initial implementation. I did switch the spin unlock to regular ST after initial experimenting, but missed this one. I'll take it out in next version. -Vineet -- 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/