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Tue, 17 Jul 2018 15:43:27 GMT Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id w6HFhOFU019170; Tue, 17 Jul 2018 15:43:25 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 17 Jul 2018 08:43:24 -0700 Subject: Re: [PATCH v13 07/18] x86/xen/time: output xen sched_clock time from 0 To: Pavel Tatashin , steven.sistare@oracle.com, daniel.m.jordan@oracle.com, linux@armlinux.org.uk, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, john.stultz@linaro.org, sboyd@codeaurora.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, douly.fnst@cn.fujitsu.com, peterz@infradead.org, prarit@redhat.com, feng.tang@intel.com, pmladek@suse.com, gnomes@lxorguk.ukuu.org.uk, linux-s390@vger.kernel.org, jgross@suse.com References: <20180712000419.5165-1-pasha.tatashin@oracle.com> <20180712000419.5165-8-pasha.tatashin@oracle.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180712000419.5165-8-pasha.tatashin@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8956 signatures=668706 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1807170164 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/11/2018 08:04 PM, Pavel Tatashin wrote: > It is expected for sched_clock() to output data from 0, when system boots. > Add an offset xen_sched_clock_offset (similarly how it is done in other > hypervisors i.e. kvm_sched_clock_offset) to count sched_clock() from 0, > when time is first initialized. > > Signed-off-by: Pavel Tatashin > --- > arch/x86/xen/time.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c > index 2ad61bf896d6..3c6f3d603373 100644 > --- a/arch/x86/xen/time.c > +++ b/arch/x86/xen/time.c > @@ -31,6 +31,8 @@ > /* Xen may fire a timer up to this many ns early */ > #define TIMER_SLOP 100000 > > +static u64 xen_sched_clock_offset __read_mostly; > + > /* Get the TSC speed from Xen */ > static unsigned long xen_tsc_khz(void) > { > @@ -57,6 +59,11 @@ static u64 xen_clocksource_get_cycles(struct clocksource *cs) > return xen_clocksource_read(); > } > > +static u64 xen_sched_clock(void) > +{ > + return xen_clocksource_read() - xen_sched_clock_offset; > +} Should other invocations of xen_clocksource_read() also be offset? -boris > + > static void xen_read_wallclock(struct timespec64 *ts) > { > struct shared_info *s = HYPERVISOR_shared_info; > @@ -367,7 +374,7 @@ void xen_timer_resume(void) > } > > static const struct pv_time_ops xen_time_ops __initconst = { > - .sched_clock = xen_clocksource_read, > + .sched_clock = xen_sched_clock, > .steal_clock = xen_steal_clock, > }; > > @@ -505,6 +512,7 @@ static void __init xen_time_init(void) > > void __init xen_init_time_ops(void) > { > + xen_sched_clock_offset = xen_clocksource_read(); > pv_time_ops = xen_time_ops; > > x86_init.timers.timer_init = xen_time_init;