From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78546C10F0E for ; Thu, 18 Apr 2019 08:57:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4621B217D7 for ; Thu, 18 Apr 2019 08:57:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YCY2bSLh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388351AbfDRI5Q (ORCPT ); Thu, 18 Apr 2019 04:57:16 -0400 Received: from merlin.infradead.org ([205.233.59.134]:37482 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388196AbfDRI5Q (ORCPT ); Thu, 18 Apr 2019 04:57:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=D7zLSethVEHi5khOP5DxgDAOzGNMwOwjlxQFcCjRB10=; b=YCY2bSLhNMwOPC9qSyTNvm8PI QgyRNywbT/boF4zeFD90uc0T9Vdm/R0M28Kj7yl3NEDh9vGEuaQ2kvv28CA9Zr+shh/ZsRwlSWsLy N5UUQBoXY4Sq0FS2CzvFblZh7Fu2dF/O4mbnWR8/RY2JELoVZ94KoiX88bBG/+wmj+wcgpLsShp9S CzB59tW4Dd08tiNwAmwDxsjXYwcKTKQcd8lFihwbxJMWbl5vkMegKxIn6Q3CjY8OxrN4idT+i5rnk KOAn5QL+jLw1UmRO1uANmxrRCQbbXgqM4Sh/nIRka9StnGWhWHKg/f/1KejQs1mVTEY0qr+ecRmVn LOAuoKH4w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hH2qt-0000k6-IL; Thu, 18 Apr 2019 08:57:03 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1F64529B98552; Thu, 18 Apr 2019 10:57:02 +0200 (CEST) Date: Thu, 18 Apr 2019 10:57:02 +0200 From: Peter Zijlstra To: Waiman Long Cc: Ingo Molnar , Will Deacon , Thomas Gleixner , linux-kernel@vger.kernel.org, x86@kernel.org, Davidlohr Bueso , Linus Torvalds , Tim Chen , huang ying Subject: Re: [PATCH v4 11/16] locking/rwsem: Enable readers spinning on writer Message-ID: <20190418085702.GW12232@hirez.programming.kicks-ass.net> References: <20190413172259.2740-1-longman@redhat.com> <20190413172259.2740-12-longman@redhat.com> <20190417135659.GH4038@hirez.programming.kicks-ass.net> <725e9765-b46e-5adb-1e81-90aefc6c38ad@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <725e9765-b46e-5adb-1e81-90aefc6c38ad@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 17, 2019 at 01:34:01PM -0400, Waiman Long wrote: > On 04/17/2019 09:56 AM, Peter Zijlstra wrote: > > On Sat, Apr 13, 2019 at 01:22:54PM -0400, Waiman Long wrote: > >> @@ -549,7 +582,7 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) > >> return !owner ? OWNER_NULL : OWNER_READER; > >> } > >> > >> -static bool rwsem_optimistic_spin(struct rw_semaphore *sem) > >> +static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock) > >> { > >> bool taken = false; > >> bool is_rt_task = rt_task(current); > >> @@ -558,9 +591,6 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem) > >> preempt_disable(); > >> > >> /* sem->wait_lock should not be held when doing optimistic spinning */ > >> - if (!rwsem_can_spin_on_owner(sem)) > >> - goto done; > >> - > >> if (!osq_lock(&sem->osq)) > >> goto done; > >> > >> @@ -580,10 +610,11 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem) > >> /* > >> * Try to acquire the lock > >> */ > >> - if (rwsem_try_write_lock_unqueued(sem)) { > >> - taken = true; > >> + taken = wlock ? rwsem_try_write_lock_unqueued(sem) > >> + : rwsem_try_read_lock_unqueued(sem); > >> + > >> + if (taken) > >> break; > >> - } > >> > >> /* > >> * An RT task cannot do optimistic spinning if it cannot > > Alternatively you pass the trylock function as an argument: > > > > static bool rwsem_optimistic_spin(struct rw_semaphore *sem, > > bool (*trylock)(struct rw_semaphore *sem)) > > { > > ... > > if (trylock(sem)) { > > taken = true; > > goto unlock; > > } > > ... > > } > > > With retpoline, an indirect function call will be slower. With compiler optimization we can avoid that. Just mark the function as __always_inline, there's only two call-sites, each with a different trylock. It might have already done that anyway, and used constant propagation on your bool, but the function pointer one is far easier to read.