From patchwork Tue Aug 27 03:21:00 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: pingfan liu X-Patchwork-Id: 270011 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)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 2FD612C00A2 for ; Tue, 27 Aug 2013 13:23:28 +1000 (EST) Received: from localhost ([::1]:53863 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VE9sM-0001wJ-Bf for incoming@patchwork.ozlabs.org; Mon, 26 Aug 2013 23:23:26 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50280) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VE9rt-0001jg-IM for qemu-devel@nongnu.org; Mon, 26 Aug 2013 23:23:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VE9rk-00064b-TE for qemu-devel@nongnu.org; Mon, 26 Aug 2013 23:22:57 -0400 Received: from mail-ob0-x229.google.com ([2607:f8b0:4003:c01::229]:57133) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VE9rk-00064X-OY for qemu-devel@nongnu.org; Mon, 26 Aug 2013 23:22:48 -0400 Received: by mail-ob0-f169.google.com with SMTP id es8so435279obc.0 for ; Mon, 26 Aug 2013 20:22:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=7km+qkUd0UJoMZsD9bN1HYRlJeyNPPd0lBWwQVt9sx8=; b=hG9AM/5+NguKJUh9ioOG/B+mXGodfzHTdM2wwBHKsJNCwC52beCQa0LSUE43cL82G0 4MHkdwLi+s3ZOr79il8x5pSw3QEKaIZJtkb8mS2tn4U018mflaFTonpJWv4zmcER9KWX QmygN4YOHefReseRx5+0Iqx3hmQBjzSUMhZ9IhMqImc9ZbwukYT/ZRgvlHQBVWqVDmLn /Cggkrxx3MkB2E1YB8U1hcch/5+KzW68mRuHHNr8/HRfC71/EcyOP+BBjyq13rDzm384 91QyBXNhFfu5Cn3pcdA/OUnjXdNzEkApAGQoHte4eooFeu3xksc+b57GBQjC4PsGSEOJ KDwg== X-Received: by 10.182.114.136 with SMTP id jg8mr171805obb.44.1377573768268; Mon, 26 Aug 2013 20:22:48 -0700 (PDT) Received: from localhost ([202.108.130.138]) by mx.google.com with ESMTPSA id a18sm17886280obf.7.1969.12.31.16.00.00 (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Mon, 26 Aug 2013 20:22:47 -0700 (PDT) From: Liu Ping Fan To: qemu-devel@nongnu.org Date: Tue, 27 Aug 2013 11:21:00 +0800 Message-Id: <1377573663-16727-2-git-send-email-pingfank@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1377573663-16727-1-git-send-email-pingfank@linux.vnet.ibm.com> References: <1377573663-16727-1-git-send-email-pingfank@linux.vnet.ibm.com> X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-Received-From: 2607:f8b0:4003:c01::229 Cc: Kevin Wolf , Paolo Bonzini , Alex Bligh , Stefan Hajnoczi , Jan Kiszka Subject: [Qemu-devel] [PATCH v3 1/4] seqlock: introduce read-write seqlock 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 From: Paolo Bonzini This lets the read-side access run outside the BQL. Signed-off-by: Paolo Bonzini --- include/qemu/seqlock.h | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 72 insertions(+) create mode 100644 include/qemu/seqlock.h diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h new file mode 100644 index 0000000..3ff118a --- /dev/null +++ b/include/qemu/seqlock.h @@ -0,0 +1,72 @@ +/* + * Seqlock implementation for QEMU + * + * Copyright Red Hat, Inc. 2013 + * + * Author: + * Paolo Bonzini + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + * + */ +#ifndef QEMU_SEQLOCK_H +#define QEMU_SEQLOCK_H 1 + +#include +#include + +typedef struct QemuSeqLock QemuSeqLock; + +struct QemuSeqLock { + QemuMutex *mutex; + unsigned sequence; +}; + +static inline void seqlock_init(QemuSeqLock *sl, QemuMutex *mutex) +{ + sl->mutex = mutex; + sl->sequence = 0; +} + +/* Lock out other writers and update the count. */ +static inline void seqlock_write_lock(QemuSeqLock *sl) +{ + if (sl->mutex) { + qemu_mutex_lock(sl->mutex); + } + ++sl->sequence; + + /* Write sequence before updating other fields. */ + smp_wmb(); +} + +static inline void seqlock_write_unlock(QemuSeqLock *sl) +{ + /* Write other fields before finalizing sequence. */ + smp_wmb(); + + ++sl->sequence; + if (sl->mutex) { + qemu_mutex_unlock(sl->mutex); + } +} + +static inline unsigned seqlock_read_begin(QemuSeqLock *sl) +{ + /* Always fail if a write is in progress. */ + unsigned ret = sl->sequence & ~1; + + /* Read sequence before reading other fields. */ + smp_rmb(); + return ret; +} + +static int seqlock_read_retry(const QemuSeqLock *sl, unsigned start) +{ + /* Read other fields before reading final sequence. */ + smp_rmb(); + return unlikely(sl->sequence != start); +} + +#endif