From patchwork Thu Jun 18 16:47:18 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Bonzini X-Patchwork-Id: 486431 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 06AF71401DA for ; Fri, 19 Jun 2015 02:53:27 +1000 (AEST) Received: from localhost ([::1]:53990 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5d49-00081Y-8j for incoming@patchwork.ozlabs.org; Thu, 18 Jun 2015 12:53:25 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56561) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5cyX-00059Q-85 for qemu-devel@nongnu.org; Thu, 18 Jun 2015 12:47:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z5cyQ-0002TZ-RM for qemu-devel@nongnu.org; Thu, 18 Jun 2015 12:47:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45164) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5cyQ-0002TR-Ew for qemu-devel@nongnu.org; Thu, 18 Jun 2015 12:47:30 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id 00F482FB8A6; Thu, 18 Jun 2015 16:47:29 +0000 (UTC) Received: from donizetti.redhat.com (ovpn-112-57.ams2.redhat.com [10.36.112.57]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t5IGlQG4014912; Thu, 18 Jun 2015 12:47:28 -0400 From: Paolo Bonzini To: qemu-devel@nongnu.org Date: Thu, 18 Jun 2015 18:47:18 +0200 Message-Id: <1434646046-27150-2-git-send-email-pbonzini@redhat.com> In-Reply-To: <1434646046-27150-1-git-send-email-pbonzini@redhat.com> References: <1434646046-27150-1-git-send-email-pbonzini@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: jan.kiszka@siemens.com Subject: [Qemu-devel] [PATCH 1/9] main-loop: use qemu_mutex_lock_iothread consistently 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 The next patch will require the BQL to be always taken with qemu_mutex_lock_iothread(), while right now this isn'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! Signed-off-by: Paolo Bonzini --- cpus.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) } else { diff --git a/cpus.c b/cpus.c index de6469f..2e807f9 100644 --- a/cpus.c +++ b/cpus.c @@ -924,7 +924,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg) CPUState *cpu = arg; int r; - qemu_mutex_lock(&qemu_global_mutex); + qemu_mutex_lock_iothread(); qemu_thread_get_self(cpu->thread); cpu->thread_id = qemu_get_thread_id(); cpu->can_do_io = 1; @@ -1004,10 +1004,10 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) { CPUState *cpu = arg; + qemu_mutex_lock_iothread(); qemu_tcg_init_cpu_signals(); qemu_thread_get_self(cpu->thread); - qemu_mutex_lock(&qemu_global_mutex); CPU_FOREACH(cpu) { cpu->thread_id = qemu_get_thread_id(); cpu->created = true; @@ -1118,7 +1118,11 @@ bool qemu_in_vcpu_thread(void) void qemu_mutex_lock_iothread(void) { atomic_inc(&iothread_requesting_mutex); - if (!tcg_enabled() || !first_cpu || !first_cpu->thread) { + /* In the simple case there is no need to bump the VCPU thread out of + * TCG code execution. + */ + if (!tcg_enabled() || qemu_in_vcpu_thread() || + !first_cpu || !first_cpu->thread) { qemu_mutex_lock(&qemu_global_mutex); atomic_dec(&iothread_requesting_mutex);