From owner-freebsd-hackers@FreeBSD.ORG Tue Jun 9 11:28:48 2015 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 986AD5F7 for ; Tue, 9 Jun 2015 11:28:48 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 0B0791FC3 for ; Tue, 9 Jun 2015 11:28:47 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.14.9/8.14.9) with ESMTP id t59BSbmH040721 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Tue, 9 Jun 2015 14:28:37 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua t59BSbmH040721 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.9/Submit) id t59BSbjA040672; Tue, 9 Jun 2015 14:28:37 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 9 Jun 2015 14:28:37 +0300 From: Konstantin Belousov To: Sebastian Huber Cc: freebsd-hackers@freebsd.org, phk@phk.freebsd.dk Subject: Re: [PATCH v3] timecounters: Fix timehand generation read/write Message-ID: <20150609112837.GL2499@kib.kiev.ua> References: <1433331966-27548-1-git-send-email-sebastian.huber@embedded-brains.de> <1433838715-22850-1-git-send-email-sebastian.huber@embedded-brains.de> <20150609105526.GK2499@kib.kiev.ua> <5576C90A.9010807@embedded-brains.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5576C90A.9010807@embedded-brains.de> 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=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Jun 2015 11:28:48 -0000 On Tue, Jun 09, 2015 at 01:07:54PM +0200, Sebastian Huber wrote: > You still need the compiler memory barriers in the UP case (at least > with GCC 4.9 on PowerPC), e.g. something like this: Fair. diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c index 9dca0e8..01c61bd 100644 --- a/sys/kern/kern_tc.c +++ b/sys/kern/kern_tc.c @@ -189,6 +190,33 @@ tc_delta(struct timehands *th) tc->tc_counter_mask); } +static u_int +tc_getgen(struct timehands *th) +{ + +#ifdef SMP + return (atomic_load_acq_int(&th->th_generation)); +#else + u_int gen; + + gen = th->th_generation; + __compiler_membar(); + return (gen); +#endif +} + +static void +tc_setgen(struct timehands *th, u_int newgen) +{ + +#ifdef SMP + atomic_store_rel_int(&th->th_generation, newgen); +#else + __compiler_membar(); + th->th_generation = newgen; +#endif +} + /* * Functions for reading the time. We have to loop until we are sure that * the timehands that we operated on was not updated under our feet. See