From mboxrd@z Thu Jan 1 00:00:00 1970 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) From: Liu Ping Fan Date: Tue, 27 Aug 2013 11:21:00 +0800 Message-Id: <1377573663-16727-2-git-send-email-pingfank@linux.vnet.ibm.com> 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> Subject: [Qemu-devel] [PATCH v3 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 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 -- 1.8.1.4