From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752556AbbKJMgO (ORCPT ); Tue, 10 Nov 2015 07:36:14 -0500 Received: from mout.kundenserver.de ([212.227.17.13]:61252 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751027AbbKJMgN (ORCPT ); Tue, 10 Nov 2015 07:36:13 -0500 From: Arnd Bergmann To: linux-arm-kernel@lists.infradead.org Cc: Stefano Stabellini , xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org, Ian.Campbell@citrix.com Subject: Re: [PATCH v2 6/7] xen/arm: introduce xen_read_wallclock Date: Tue, 10 Nov 2015 13:35:41 +0100 Message-ID: <3711503.LuojCRibK3@wuerfel> User-Agent: KMail/4.11.5 (Linux/3.16.0-10-generic; KDE/4.11.5; x86_64; ; ) In-Reply-To: <1447156675-7418-6-git-send-email-stefano.stabellini@eu.citrix.com> References: <1447156675-7418-6-git-send-email-stefano.stabellini@eu.citrix.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V03:K0:xmpAnlwBegDOR2yoG+Uu8fjfOxJLHO13WV4ergcSksy2fROFdiG R277ggt0cKH4cYL/XhqCDedn/W2PEgnIKheJNahsA7kZtHtbqT4G5l1J5ZW/w3HE6O3r/Jd NVJe0bj23yhYEqbwaykmqbndMW1Ky9gawK3cXbg97MTdrJbHUtR7A5cwkKzjzWh7ZCu8Y1n 8Zwp30HDZG6HkyDuYoe5Q== X-UI-Out-Filterresults: notjunk:1;V01:K0:960zrcuZx7c=:K4WIHvgPjMt/tQ5b8DevpU s8uxR5EATane1bTyN1x2tOs+n9mrmvit3T8L2lP85PSUGLEgiAb9RzH+x35yNE8Maje6tRsEh KY8K9W8xfkwmF4UuX45tvoHuSDSUxoXVUj9L+Tw3czldIEtMq5lLN7MAZoNYBXW3FjFZguptm Z/JZOxJmEXgOf7b+1Y+KZPj2Pq5eiOaTXl1wyMGRaDduMDy5Kug1r0/Ip1oMGfVFnFDcK5nnB G6sxs2xpeNwcixCITvBlpq5DvhEqJzfNr66tNn1mtywBg0Q+5p9Jj760Zhij46Asj+0xz4jq/ R9etvpYbFAuvOkwXMpPK0qG4xx0MlH4Sf63uZvqrTRLE/nzj0EqwyaiOuuB9+SLb13hZf1Lq2 j2MEmwQcvmwIqlOznV7zNqWT3Ky8MhmMNeWLrzNdvVZaqXB9HpPItGDhElWqOadLO3EbYTLHS /8321UdDHHxVg4IWCpo263TED09UIjqD+SiVXO/ek9S8US9sbFyD9w0x35FloB5dyXKUo5QAQ lElD4qQ1d6y+BkK3c8XnQLmT1SgqTK/xAGnEyV3QyabpED9jIdf6fIOtnTB3ieNMT73oEUeBo 2UrmqfZCdckFoufGV/8xlpbT1rjGdU0GVb7Yiu2VZCCvz+H/hJd9wSDRynf6XsNBIFpYAyHXU wzjHlkYH9H9lSgTCooTqY9b7e4Jz2W/KdNtuqYxn+YpwuHmNkLX2XrW4HpTGSO4gcTzhUv0oz o72rKcXfc/KrheMn Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 10 November 2015 11:57:54 Stefano Stabellini wrote: > +static void xen_read_wallclock(struct timespec64 *ts) > +{ > + u32 version; > + u64 delta; > + struct timespec64 now; > + struct shared_info *s = HYPERVISOR_shared_info; > + struct pvclock_wall_clock *wall_clock = &(s->wc); > + > + /* get wallclock at system boot */ > + do { > + version = wall_clock->version; > + rmb(); /* fetch version before time */ > + now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | wall_clock->sec; > + now.tv_nsec = wall_clock->nsec; > + rmb(); /* fetch time before checking version */ > + } while ((wall_clock->version & 1) || (version != wall_clock->version)); > + > + delta = arch_timer_read_counter() * (u64)NSEC_PER_SEC; > + do_div(delta, arch_timer_get_rate()); /* time since system boot */ > + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; > + > + now.tv_nsec = do_div(delta, NSEC_PER_SEC); > + now.tv_sec = delta; > + > + set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec); > + > +} Instead of the two do_div(), I would do the entire calculation in terms of nanoseconds and then call ns_to_timespec64() in the end instead of set_normalized_timespec64(). That is just an optimization though, your version looks correct as well. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Tue, 10 Nov 2015 13:35:41 +0100 Subject: [PATCH v2 6/7] xen/arm: introduce xen_read_wallclock In-Reply-To: <1447156675-7418-6-git-send-email-stefano.stabellini@eu.citrix.com> References: <1447156675-7418-6-git-send-email-stefano.stabellini@eu.citrix.com> Message-ID: <3711503.LuojCRibK3@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tuesday 10 November 2015 11:57:54 Stefano Stabellini wrote: > +static void xen_read_wallclock(struct timespec64 *ts) > +{ > + u32 version; > + u64 delta; > + struct timespec64 now; > + struct shared_info *s = HYPERVISOR_shared_info; > + struct pvclock_wall_clock *wall_clock = &(s->wc); > + > + /* get wallclock at system boot */ > + do { > + version = wall_clock->version; > + rmb(); /* fetch version before time */ > + now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | wall_clock->sec; > + now.tv_nsec = wall_clock->nsec; > + rmb(); /* fetch time before checking version */ > + } while ((wall_clock->version & 1) || (version != wall_clock->version)); > + > + delta = arch_timer_read_counter() * (u64)NSEC_PER_SEC; > + do_div(delta, arch_timer_get_rate()); /* time since system boot */ > + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; > + > + now.tv_nsec = do_div(delta, NSEC_PER_SEC); > + now.tv_sec = delta; > + > + set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec); > + > +} Instead of the two do_div(), I would do the entire calculation in terms of nanoseconds and then call ns_to_timespec64() in the end instead of set_normalized_timespec64(). That is just an optimization though, your version looks correct as well. Arnd