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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AEE32C43334 for ; Tue, 12 Jul 2022 00:50:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231208AbiGLAug (ORCPT ); Mon, 11 Jul 2022 20:50:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51690 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229743AbiGLAue (ORCPT ); Mon, 11 Jul 2022 20:50:34 -0400 Received: from mail-pl1-x630.google.com (mail-pl1-x630.google.com [IPv6:2607:f8b0:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 39FA9248E1 for ; Mon, 11 Jul 2022 17:50:34 -0700 (PDT) Received: by mail-pl1-x630.google.com with SMTP id z1so5890812plb.1 for ; Mon, 11 Jul 2022 17:50:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:subject:to:cc:references:in-reply-to:mime-version :message-id:content-transfer-encoding; bh=nq5VDTxnZLTeB3sMypNbVikOvabvDzmucjQyVWV8Mbw=; b=ZNcOdc0oHW7mvchFZZ3WG4YtzPiUj5LGAp3PVmSX1JTAaQkK0VocOEHQRn0ioDkAD/ LVQm28xLDyvplVuV4zehdCLo55A51S6LbFI6BCPsI6EGdUtipoMv+Jvpy+Zg2jLfpbZQ lMjyxEmlGl0xfAN4ErdnVKzoHLpNTSfyXSdUvo33XocZAtAScDVZQm02ircDLxCxZ/rL 6l51AKmZ6YR3TS/qtUyvKt49EZHaXXq0LWJaQy2NjkP6k07C9PcUykxzRvNqhHadE7uH 8j02N3ms/F03A+wWHaxpTllOl7u2Pj1Vy690icO6TvwCfHl2HiCS6yr2k1mDgxQWVxd6 DYYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:subject:to:cc:references:in-reply-to :mime-version:message-id:content-transfer-encoding; bh=nq5VDTxnZLTeB3sMypNbVikOvabvDzmucjQyVWV8Mbw=; b=qBgb1SEWE6jPHxwtMD9RoyGz9Z2jhil/uB3wGOD7uMao/gfUWq3RNTuoUUolDJWyPM ChTa9Ii8/4iiTEhTiUfqea9B4T0Hr4rOqQVIPxX5srut5rPWM0iRPEWdPldvm4txnAvQ ZhRA326jfJX0kA5BaOb9/ae436B7d9FE4YCi8qC6Bbs7ZQINX+redQl3z7KRyuQsPdP+ feVqqmSXVO57czGf95LxW8ei0QTHnBUyuUOPDcAoHZR8M84ODmcMcE3jP+fWlb29n6gV vuHfK/tkHfOAr3h5IC9RRzfSLGAWKYoO5ZxmQV759DsYaIC4ljSdq6U+NbJSl0FhX2ch L4zg== X-Gm-Message-State: AJIora+gHI8DaWHZAqdj2wFgrzSaCGg0435nmYgJoOAIJWxHM0ApX8dj VXMXT3U0faMiGy67Hq8n1uQ= X-Google-Smtp-Source: AGRyM1sEEa926e/qwc78doygaREQbplTVW9CcC3PGLsudg2YHFDq9IlA2rYG7qhcIPCSCSpNd1pnIQ== X-Received: by 2002:a17:903:1c4:b0:16c:4e45:38a3 with SMTP id e4-20020a17090301c400b0016c4e4538a3mr6635115plh.41.1657587033798; Mon, 11 Jul 2022 17:50:33 -0700 (PDT) Received: from localhost (193-116-203-247.tpgi.com.au. [193.116.203.247]) by smtp.gmail.com with ESMTPSA id i14-20020a170902c94e00b0016c4331e61csm3314982pla.137.2022.07.11.17.50.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 Jul 2022 17:50:33 -0700 (PDT) Date: Tue, 12 Jul 2022 10:50:28 +1000 From: Nicholas Piggin Subject: Re: [PATCH 12/13] locking/qspinlock: separate pv_wait_node from the non-paravirt path To: Peter Zijlstra Cc: Boqun Feng , linux-kernel@vger.kernel.org, Waiman Long , Ingo Molnar , Will Deacon References: <20220704143820.3071004-1-npiggin@gmail.com> <20220704143820.3071004-13-npiggin@gmail.com> In-Reply-To: MIME-Version: 1.0 Message-Id: <1657586928.uawdad42k7.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Excerpts from Peter Zijlstra's message of July 6, 2022 3:34 am: > On Tue, Jul 05, 2022 at 12:38:19AM +1000, Nicholas Piggin wrote: >> pv_wait_node waits until node->locked is non-zero, no need for the >> pv case to wait again by also executing the !pv code path. >>=20 >> Signed-off-by: Nicholas Piggin >> --- >> kernel/locking/qspinlock.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >>=20 >> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c >> index 9db168753124..19e2f286be0a 100644 >> --- a/kernel/locking/qspinlock.c >> +++ b/kernel/locking/qspinlock.c >> @@ -862,10 +862,11 @@ static inline void queued_spin_lock_mcs_queue(stru= ct qspinlock *lock, bool parav >> /* Link @node into the waitqueue. */ >> WRITE_ONCE(prev->next, node); >> =20 >> + /* Wait for mcs node lock to be released */ >> if (paravirt) >> pv_wait_node(node, prev); >> - /* Wait for mcs node lock to be released */ >> - smp_cond_load_acquire(&node->locked, VAL); >> + else >> + smp_cond_load_acquire(&node->locked, VAL); >> =20 >=20 > (from patch #6): >=20 > +static void pv_wait_node(struct qnode *node, struct qnode *prev) > +{ > + int loop; > + bool wait_early; > + > ... > + > + /* > + * By now our node->locked should be 1 and our caller will not ac= tually > + * spin-wait for it. We do however rely on our caller to do a > + * load-acquire for us. > + */ > +} >=20 >=20 Oh good catch, thanks so much that's a dumb bug. I'll add a=20 smp_load_acquire at the end of pv_wait_node where that comment is. Thanks, Nick