From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50271) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VNelc-0000nz-AP for qemu-devel@nongnu.org; Sun, 22 Sep 2013 04:11:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VNelT-0006oc-P1 for qemu-devel@nongnu.org; Sun, 22 Sep 2013 04:11:44 -0400 Received: from mail-ie0-x232.google.com ([2607:f8b0:4001:c03::232]:50338) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VNelT-0006oY-KM for qemu-devel@nongnu.org; Sun, 22 Sep 2013 04:11:35 -0400 Received: by mail-ie0-f178.google.com with SMTP id to1so4390569ieb.9 for ; Sun, 22 Sep 2013 01:11:35 -0700 (PDT) From: Liu Ping Fan Date: Sun, 22 Sep 2013 16:11:16 +0800 Message-Id: <1379837479-8419-3-git-send-email-pingfank@linux.vnet.ibm.com> In-Reply-To: <1379837479-8419-1-git-send-email-pingfank@linux.vnet.ibm.com> References: <1379837479-8419-1-git-send-email-pingfank@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH v4 1/4] seqlock: introduce read-write seqlock List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Kevin Wolf , Paolo Bonzini , Alex Bligh , Stefan Hajnoczi , Jan Kiszka 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 -- 1.8.1.4