From owner-freebsd-arch@FreeBSD.ORG Sat Aug 16 09:38:17 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 CEB3F515; Sat, 16 Aug 2014 09:38:17 +0000 (UTC) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 6C5A52568; Sat, 16 Aug 2014 09:38:17 +0000 (UTC) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.14.9/8.14.9) with ESMTP id s7G9cBvv076919 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sat, 16 Aug 2014 12:38:12 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua s7G9cBvv076919 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.9/Submit) id s7G9cBN0076918; Sat, 16 Aug 2014 12:38:11 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 16 Aug 2014 12:38:11 +0300 From: Konstantin Belousov To: Mateusz Guzik Subject: Re: [PATCH 1/2] Implement simple sequence counters with memory barriers. Message-ID: <20140816093811.GX2737@kib.kiev.ua> References: <1408064112-573-1-git-send-email-mjguzik@gmail.com> <1408064112-573-2-git-send-email-mjguzik@gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="BkCcXYe/IK2urb/q" Content-Disposition: inline In-Reply-To: <1408064112-573-2-git-send-email-mjguzik@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.0 X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on tom.home Cc: Konstantin Belousov , Johan Schuijt , freebsd-arch@freebsd.org 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: Sat, 16 Aug 2014 09:38:18 -0000 --BkCcXYe/IK2urb/q Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Aug 15, 2014 at 02:55:11AM +0200, Mateusz Guzik wrote: > --- > sys/sys/seq.h | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++= ++++++ > 1 file changed, 126 insertions(+) > create mode 100644 sys/sys/seq.h >=20 > 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 distributio= n. > + * > + * 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 PU= RPOSE > + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIAB= LE > + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUE= NTIAL > + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOO= DS > + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) > + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, S= TRICT > + * 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 =3D seq_read(&gobj->seq); > + * lobj =3D gobj; > + * if (seq_consistent(&gobj->seq, seq)) > + * break; > + * cpu_spinwait(); > + * } > + * foo(lobj); > + */ =09 > + > +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(); This probably ought to be written as atomic_add_rel_int(seqp, 1); Same note for all other linux-style barriers. In fact, on x86 wmb() is sfence and it serves no useful purpose in seq_write*. Overall, it feels too alien and linux-ish for my taste. Since we have sequence bound to some lock anyway, could we introduce some sort of generation-aware locks variants, which extend existing locks, and where lock/unlock bump generation number ? > +} > + > +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 =3D 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 =3D=3D 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_ */ > --=20 > 2.0.2 --BkCcXYe/IK2urb/q Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBAgAGBQJT7yaDAAoJEJDCuSvBvK1BTRMP/1ECsFOhc06qSXshkUgScpQ7 xbAghb6WYTI/I4Es3w9aBq6AxK1YfaxjW0Liv0/YFAkkUnSU9Ko6xpoY2QZDBkv/ 5BxCA8Qd5F02GDz7lnPt2iiCevDJXmGQqEtt3VKzE26eoinJX38v1lKvFSTMAXKq UXZ9YIsL5TrLUECoM+UuB5CtPbD7/TtQ2W6XBgqCKYGxjy9zWHysRWi8sej0kwst 3zzztnCaRGSNwDhnaKfZND21QVzmMx6budSi6Q5/UjBiFrIBXtJ+Ioq7bc+tmiOO dTUq2BFyhkN+LgqSLK/+2X8dT0qemwrJWzuAw2tcxzx6Wdq0zPAmwtZgyPar+rZh fdrbXnSHXhMaBaqZJsVyp6BRZ+TfSRNQ+wWaYdFcsme9OTMe7ciZCxaCKCYho8dX yE38GOmziBWRqu0LbL1fhQuc1XE5RmaMiUR6MEyfa/t2/RjLJJEVJ3ec+1esLB0W CdwrXeObDMMqE/IWxVIteEWOPI88r/RkNcjnLOm6aJ4JGvvqiE+ugVlsIsLZI2Qp P+Cq8+afDsQRWbwi6jZjESx1W3XecwhAcLvjLpu4KXICi8QJSCwxfMjU9pUR0weD npK1C70skOqJCi4Ty7oDHrmmUAt6NueMMIbESBfbwae/CnrQSHdii4Oc1s5X/G2+ yQmbWjUPT6CLXaLfv5fH =LoS0 -----END PGP SIGNATURE----- --BkCcXYe/IK2urb/q--