From patchwork Wed Jun 24 16:25:03 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Bonzini X-Patchwork-Id: 488146 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id EDC5614030F for ; Thu, 25 Jun 2015 02:29:37 +1000 (AEST) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b=XDxgysY6; dkim-atps=neutral Received: from localhost ([::1]:51852 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7nYO-0008Ir-5c for incoming@patchwork.ozlabs.org; Wed, 24 Jun 2015 12:29:36 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56337) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7nUJ-00014L-RR for qemu-devel@nongnu.org; Wed, 24 Jun 2015 12:25:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z7nUE-0003fM-2g for qemu-devel@nongnu.org; Wed, 24 Jun 2015 12:25:23 -0400 Received: from mail-wi0-x234.google.com ([2a00:1450:400c:c05::234]:34810) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7nUD-0003f3-Sn for qemu-devel@nongnu.org; Wed, 24 Jun 2015 12:25:18 -0400 Received: by wicnd19 with SMTP id nd19so139704161wic.1 for ; Wed, 24 Jun 2015 09:25:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=xUvNLGFnjwSJacJERmL3jz3btYSpqAlmTC2i/JSmBIY=; b=XDxgysY6wIBzxhkXYQk0KGVVEaLCmWnPhOpvAo06/FWSG635K96m9s0s8DsRtD7JYJ /3JilfGVH25wGL6kxncpMZS8lNthALKBK3qsQZFmsvQxf7s4f6pEGDvu/ULBkyvTz1Ts JB6yAg22Jwiak8XEyNgSfwTBNdMPl1pyn6JL/pb33LBkf7urP/cR5F4M+2B9MTXXuc7i rUXgjZDVp0Dn+g86oGzBHXrr31f/O2nJ0E/mf7HD+UKmT6aHeKGDZMgrPWO+QMELGiGf DwJ9ll5nFY6lUXejouV2Vbcv5avpSGb0RBA/+FVPQzX01mCsPJu67mJHZ42f3Po44Zep cXeg== X-Received: by 10.180.219.42 with SMTP id pl10mr6482476wic.70.1435163117334; Wed, 24 Jun 2015 09:25:17 -0700 (PDT) Received: from 640k.localdomain (dynamic-adsl-94-39-132-37.clienti.tiscali.it. [94.39.132.37]) by mx.google.com with ESMTPSA id gt10sm3305953wib.20.2015.06.24.09.25.16 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Jun 2015 09:25:16 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Date: Wed, 24 Jun 2015 18:25:03 +0200 Message-Id: <1435163110-2724-3-git-send-email-pbonzini@redhat.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1435163110-2724-1-git-send-email-pbonzini@redhat.com> References: <1435163110-2724-1-git-send-email-pbonzini@redhat.com> X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-Received-From: 2a00:1450:400c:c05::234 Cc: borntraeger@de.ibm.com, famz@redhat.com, Frederic Konrad Subject: [Qemu-devel] [PATCH 2/9] main-loop: introduce qemu_mutex_iothread_locked X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org This function will be used to avoid recursive locking of the iothread lock whenever address_space_rw/ld*/st* are called with the BQL held, which is almost always the case. Tracking whether the iothread is owned is very cheap (just use a TLS variable) but requires some care because now the lock must always be taken with qemu_mutex_lock_iothread(). Previously this wasn't the case. Outside TCG mode this is not a problem. In TCG mode, we need to be careful and avoid the "prod out of compiled code" step if already in a VCPU thread. This is easily done with a check on current_cpu, i.e. qemu_in_vcpu_thread(). Hopefully, multithreaded TCG will get rid of the whole logic to kick VCPUs whenever an I/O event occurs! Cc: Frederic Konrad Message-Id: <1434646046-27150-3-git-send-email-pbonzini@redhat.com> Reviewed-by: Fam Zheng Signed-off-by: Paolo Bonzini --- cpus.c | 9 +++++++++ include/qemu/main-loop.h | 10 ++++++++++ stubs/iothread-lock.c | 5 +++++ 3 files changed, 24 insertions(+) diff --git a/cpus.c b/cpus.c index 02cca5d..29fc2dd 100644 --- a/cpus.c +++ b/cpus.c @@ -1145,6 +1145,13 @@ bool qemu_in_vcpu_thread(void) return current_cpu && qemu_cpu_is_self(current_cpu); } +static __thread bool iothread_locked = false; + +bool qemu_mutex_iothread_locked(void) +{ + return iothread_locked; +} + void qemu_mutex_lock_iothread(void) { atomic_inc(&iothread_requesting_mutex); @@ -1163,10 +1170,12 @@ void qemu_mutex_lock_iothread(void) atomic_dec(&iothread_requesting_mutex); qemu_cond_broadcast(&qemu_io_proceeded_cond); } + iothread_locked = true; } void qemu_mutex_unlock_iothread(void) { + iothread_locked = false; qemu_mutex_unlock(&qemu_global_mutex); } diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h index 0f4a0fd..bc18ca3 100644 --- a/include/qemu/main-loop.h +++ b/include/qemu/main-loop.h @@ -223,6 +223,16 @@ int qemu_add_child_watch(pid_t pid); #endif /** + * qemu_mutex_iothread_locked: Return lock status of the main loop mutex. + * + * The main loop mutex is the coarsest lock in QEMU, and as such it + * must always be taken outside other locks. This function helps + * functions take different paths depending on whether the current + * thread is running within the main loop mutex. + */ +bool qemu_mutex_iothread_locked(void); + +/** * qemu_mutex_lock_iothread: Lock the main loop mutex. * * This function locks the main loop mutex. The mutex is taken by diff --git a/stubs/iothread-lock.c b/stubs/iothread-lock.c index 5d8aca1..dda6f6b 100644 --- a/stubs/iothread-lock.c +++ b/stubs/iothread-lock.c @@ -1,6 +1,11 @@ #include "qemu-common.h" #include "qemu/main-loop.h" +bool qemu_mutex_iothread_locked(void) +{ + return true; +} + void qemu_mutex_lock_iothread(void) { }