From patchwork Tue Oct 31 11:07:51 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Pavel Dovgalyuk X-Patchwork-Id: 117578 Delivered-To: patch@linaro.org Received: by 10.80.245.45 with SMTP id t42csp3822404edm; Tue, 31 Oct 2017 04:18:41 -0700 (PDT) X-Google-Smtp-Source: ABhQp+RaVzmZ8cUWnUKRkicFSIgwVzAKkbaaCBq0D8xZKjEKaRrctEHnlczy8NcWSY+RwdH+NlD8 X-Received: by 10.129.4.206 with SMTP id 197mr956857ywe.45.1509448721615; Tue, 31 Oct 2017 04:18:41 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1509448721; cv=none; d=google.com; s=arc-20160816; b=pMJjCR4RTrWnNMrahO6pxJ5E8cSZLzoU30GKMxwtyWliv5SmPIEemL24Wg6c8azaUs BolDnVyAbY/dvpBE39k9QdUeLNoJWH73f6Oc8YdlRAMffiwozOMSdH4AChhZKkZwiOgq DZ5djR9/rllWqzV/Uj/eaJt7tOKLLIR81UlthO7yBqcGMWioxRmuM0E6herp5CTgrOig w3JybqjxApezi35DuIzkEO7TKhCreXdXzGITyhTD/4yT65N71DYhk0Ih0VTlQG5/lv6/ VLYcTlMbaxGcEs6Webp7TC3zeWUrSJyrY57CB5pNOYzlXegpQUCSFxO6tMopDLqHeyQX XDwQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=sender:errors-to:cc:list-subscribe:list-help:list-post:list-archive :list-unsubscribe:list-id:precedence:subject :content-transfer-encoding:mime-version:user-agent:references :in-reply-to:message-id:date:to:from:arc-authentication-results; bh=8W/ovF+pNP4R6zkQ0YBiysLimkvlkFH3QXx5jt6gKCA=; b=wsJ7QOSd5K5c/3L8ro7oJGE797KNzwB0HgFxDjhQ7B3+X7OR/vQW9vZCaxhxmXjINK PjS0zj/nW6PaF/QYPWVNQwy/U+0T4L7ytzeNZIUb6PH0ZXtNq5S3wK4AZ5gOb4R3PNDl t1gCjNNmb8IDhD9m5qCldqutC6jozyBAizZqMogEKSe0BE72XjtxkHsnavH1OmmJ615l tYJTa7iKsiL6xWjmebcxVXfiHMvcgIzyE/3OmOeedu3a9424FK0JSiI5f27XsR7KSK+K 1Vnx6O44gZiJuCm2o+Yy2Ce+TOz7uAo4p4jgGf3Wyz57KSRlaaOb8qikR0vbtbkxIDt8 8CXw== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) smtp.mailfrom=qemu-devel-bounces+patch=linaro.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org. [2001:4830:134:3::11]) by mx.google.com with ESMTPS id z189si339568ybz.146.2017.10.31.04.18.41 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 31 Oct 2017 04:18:41 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) client-ip=2001:4830:134:3::11; Authentication-Results: mx.google.com; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) smtp.mailfrom=qemu-devel-bounces+patch=linaro.org@nongnu.org Received: from localhost ([::1]:44830 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e9UZ6-00061c-V0 for patch@linaro.org; Tue, 31 Oct 2017 07:18:41 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39721) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e9UOe-0004gB-MI for qemu-devel@nongnu.org; Tue, 31 Oct 2017 07:07:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e9UOd-0006wZ-Hh for qemu-devel@nongnu.org; Tue, 31 Oct 2017 07:07:52 -0400 Received: from mail.ispras.ru ([83.149.199.45]:42306) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e9UOd-0006w6-9T for qemu-devel@nongnu.org; Tue, 31 Oct 2017 07:07:51 -0400 Received: from [127.0.1.1] (unknown [85.142.117.226]) by mail.ispras.ru (Postfix) with ESMTPSA id A55D454006A; Tue, 31 Oct 2017 14:07:50 +0300 (MSK) From: Pavel Dovgalyuk To: qemu-devel@nongnu.org Date: Tue, 31 Oct 2017 14:07:51 +0300 Message-ID: <20171031110751.5836.64445.stgit@pasha-VirtualBox> In-Reply-To: <20171031110641.5836.43266.stgit@pasha-VirtualBox> References: <20171031110641.5836.43266.stgit@pasha-VirtualBox> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 83.149.199.45 Subject: [Qemu-devel] [RFC PATCH 13/26] cpus: only take BQL for sleeping threads X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: dovgaluk@ispras.ru Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: "Qemu-devel" From: Alex Bennée Now the only real need to hold the BQL is for when we sleep on the cpu->halt conditional. The lock is actually dropped while the thread sleeps so the actual window for contention is pretty small. This also means we can remove the special case hack for exclusive work and simply declare that work no longer has an implicit BQL held. This isn't a major problem async work is generally only changing things in the context of its own vCPU. If it needs to work across vCPUs it should be using the exclusive mechanism or possibly taking the lock itself. Signed-off-by: Alex Bennée --- cpus-common.c | 13 +++++-------- cpus.c | 10 ++++------ 2 files changed, 9 insertions(+), 14 deletions(-) diff --git a/cpus-common.c b/cpus-common.c index 59f751e..64661c3 100644 --- a/cpus-common.c +++ b/cpus-common.c @@ -310,6 +310,11 @@ void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, queue_work_on_cpu(cpu, wi); } +/* Work items run outside of the BQL. This is essential for avoiding a + * deadlock for exclusive work but also applies to non-exclusive work. + * If the work requires cross-vCPU changes then it should use the + * exclusive mechanism. + */ void process_queued_cpu_work(CPUState *cpu) { struct qemu_work_item *wi; @@ -327,17 +332,9 @@ void process_queued_cpu_work(CPUState *cpu) } qemu_mutex_unlock(&cpu->work_mutex); if (wi->exclusive) { - /* Running work items outside the BQL avoids the following deadlock: - * 1) start_exclusive() is called with the BQL taken while another - * CPU is running; 2) cpu_exec in the other CPU tries to takes the - * BQL, so it goes to sleep; start_exclusive() is sleeping too, so - * neither CPU can proceed. - */ - qemu_mutex_unlock_iothread(); start_exclusive(); wi->func(cpu, wi->data); end_exclusive(); - qemu_mutex_lock_iothread(); } else { wi->func(cpu, wi->data); } diff --git a/cpus.c b/cpus.c index efde5c1..de6dfce 100644 --- a/cpus.c +++ b/cpus.c @@ -1127,31 +1127,29 @@ static bool qemu_tcg_should_sleep(CPUState *cpu) static void qemu_tcg_wait_io_event(CPUState *cpu) { - qemu_mutex_lock_iothread(); while (qemu_tcg_should_sleep(cpu)) { + qemu_mutex_lock_iothread(); stop_tcg_kick_timer(); qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex); + qemu_mutex_unlock_iothread(); } start_tcg_kick_timer(); qemu_wait_io_event_common(cpu); - - qemu_mutex_unlock_iothread(); } static void qemu_kvm_wait_io_event(CPUState *cpu) { - qemu_mutex_lock_iothread(); while (cpu_thread_is_idle(cpu)) { + qemu_mutex_lock_iothread(); qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex); + qemu_mutex_unlock_iothread(); } qemu_wait_io_event_common(cpu); - - qemu_mutex_unlock_iothread(); } static void *qemu_kvm_cpu_thread_fn(void *arg)