From owner-freebsd-arch@FreeBSD.ORG Fri Aug 15 00:55:19 2014 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 17DA396; Fri, 15 Aug 2014 00:55:19 +0000 (UTC) Received: from mail-we0-x22a.google.com (mail-we0-x22a.google.com [IPv6:2a00:1450:400c:c03::22a]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 38106290F; Fri, 15 Aug 2014 00:55:18 +0000 (UTC) Received: by mail-we0-f170.google.com with SMTP id w62so1807079wes.15 for ; Thu, 14 Aug 2014 17:55:16 -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=6yC0IPWCG3qT4LJ9DTzfFywurlLVSsr7jPiw7ugjI2g=; b=VYeLey3N1+/B7bh8JwtEdLakxxNiRjUOnt1vi7PbBQDdMC9QVn9LrBDcUTgKT7Eiq6 2f8VYzV4jmdYEEqLXEiL3fZwF17vtaoeoBzqGve2XY2Ji1yX4Rg7/UJnpflU2y6R48yE eJ4LOldJ4e/Q+64nS/26IHJc52heudjM4TxV3dtUAZieWKZfzJOsv8zoDHbX1fGw/+NT DlohW4xG+IqQxdG/WZ4b39kj5gWHK5xye2CJOo6lqkhGB1L39Uh9CPOJbv15DODPxDr9 02aZmkmJ/B/89nfPuW2o4IL1+SxMj99c5IJymdhL0YK6lc4dCBYDWlRfrQl4HmSkYx0u v9vQ== X-Received: by 10.194.203.105 with SMTP id kp9mr16985375wjc.41.1408064116467; Thu, 14 Aug 2014 17:55:16 -0700 (PDT) Received: from localhost.localdomain (ip-62-245-66-51.net.upcbroadband.cz. [62.245.66.51]) by mx.google.com with ESMTPSA id fp6sm1473669wic.11.2014.08.14.17.55.14 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 Aug 2014 17:55:15 -0700 (PDT) From: Mateusz Guzik To: freebsd-arch@freebsd.org Subject: [PATCH 1/2] Implement simple sequence counters with memory barriers. Date: Fri, 15 Aug 2014 02:55:11 +0200 Message-Id: <1408064112-573-2-git-send-email-mjguzik@gmail.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1408064112-573-1-git-send-email-mjguzik@gmail.com> References: <1408064112-573-1-git-send-email-mjguzik@gmail.com> Cc: Robert Watson , Johan Schuijt , Konstantin Belousov X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Aug 2014 00:55:19 -0000 --- sys/sys/seq.h | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 126 insertions(+) create mode 100644 sys/sys/seq.h diff --git a/sys/sys/seq.h b/sys/sys/seq.h new file mode 100644 index 0000000..0971aef --- /dev/null +++ b/sys/sys/seq.h @@ -0,0 +1,126 @@ +/*- + * Copyright (c) 2014 The FreeBSD Project + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + * + * $FreeBSD$ + */ + +#ifndef _SYS_SEQ_H_ +#define _SYS_SEQ_H_ + +#ifdef _KERNEL + +/* + * Typical usage: + * + * writers: + * lock_exclusive(&obj->lock); + * seq_write_begin(&obj->seq); + * ..... + * seq_write_end(&obj->seq); + * unlock_exclusive(&obj->unlock); + * + * readers: + * obj_t lobj; + * seq_t seq; + * + * for (;;) { + * seq = seq_read(&gobj->seq); + * lobj = gobj; + * if (seq_consistent(&gobj->seq, seq)) + * break; + * cpu_spinwait(); + * } + * foo(lobj); + */ + +typedef uint32_t seq_t; + +/* A hack to get MPASS macro */ +#include +#include + +#include + +static __inline bool +seq_in_modify(seq_t seqp) +{ + + return (seqp & 1); +} + +static __inline void +seq_write_begin(seq_t *seqp) +{ + + MPASS(!seq_in_modify(*seqp)); + (*seqp)++; + wmb(); +} + +static __inline void +seq_write_end(seq_t *seqp) +{ + + wmb(); + (*seqp)++; + MPASS(!seq_in_modify(*seqp)); +} + +static __inline seq_t +seq_read(seq_t *seqp) +{ + seq_t ret; + + for (;;) { + ret = READ_ONCE(*seqp); + if (seq_in_modify(ret)) { + cpu_spinwait(); + continue; + } + break; + } + + rmb(); + + return (ret); +} + +static __inline seq_t +seq_consistent_nomb(seq_t *seqp, seq_t oldseqp) +{ + + MPASS(!seq_in_modify(oldseqp)); + return (*seqp == oldseqp); +} + +static __inline seq_t +seq_consistent(seq_t *seqp, seq_t oldseqp) +{ + + rmb(); + return (seq_consistent_nomb(seqp, oldseqp)); +} + +#endif /* _KERNEL */ +#endif /* _SYS_SEQ_H_ */ -- 2.0.2