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Sat, 30 May 2020 23:33:11 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3030.oracle.com with ESMTP id 31bckr95xa-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 30 May 2020 23:33:11 +0000 Received: from abhmp0008.oracle.com (abhmp0008.oracle.com [141.146.116.14]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 04UNX2Sg027376; Sat, 30 May 2020 23:33:03 GMT Received: from [10.39.241.21] (/10.39.241.21) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sat, 30 May 2020 16:33:02 -0700 Subject: Re: [PATCH 08/12] xen/time: introduce xen_{save,restore}_steal_clock To: Anchal Agarwal , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, jgross@suse.com, linux-pm@vger.kernel.org, linux-mm@kvack.org, kamatam@amazon.com, sstabellini@kernel.org, konrad.wilk@oracle.com, roger.pau@citrix.com, axboe@kernel.dk, davem@davemloft.net, rjw@rjwysocki.net, len.brown@intel.com, pavel@ucw.cz, peterz@infradead.org, eduval@amazon.com, sblbir@amazon.com, xen-devel@lists.xenproject.org, vkuznets@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, dwmw@amazon.co.uk, benh@kernel.crashing.org References: From: Boris Ostrovsky Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9637 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 malwarescore=0 adultscore=0 suspectscore=0 mlxscore=0 spamscore=0 mlxlogscore=999 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005300184 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9637 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 suspectscore=0 mlxlogscore=999 priorityscore=1501 bulkscore=0 phishscore=0 clxscore=1015 impostorscore=0 adultscore=0 spamscore=0 mlxscore=0 lowpriorityscore=0 cotscore=-2147483648 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005300183 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/19/20 7:28 PM, Anchal Agarwal wrote: > From: Munehisa Kamata > > Currently, steal time accounting code in scheduler expects steal clock > callback to provide monotonically increasing value. If the accounting > code receives a smaller value than previous one, it uses a negative > value to calculate steal time and results in incorrectly updated idle > and steal time accounting. This breaks userspace tools which read > /proc/stat. > > top - 08:05:35 up 2:12, 3 users, load average: 0.00, 0.07, 0.23 > Tasks: 80 total, 1 running, 79 sleeping, 0 stopped, 0 zombie > Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,30100.0%id, 0.0%wa, 0.0%hi, 0.0%si,= -1253874204672.0%st > > This can actually happen when a Xen PVHVM guest gets restored from > hibernation, because such a restored guest is just a fresh domain from > Xen perspective and the time information in runstate info starts over > from scratch. > > This patch introduces xen_save_steal_clock() which saves current values= > in runstate info into per-cpu variables. Its couterpart, > xen_restore_steal_clock(), sets offset if it found the current values i= n > runstate info are smaller than previous ones. xen_steal_clock() is also= > modified to use the offset to ensure that scheduler only sees > monotonically increasing number. > > Signed-off-by: Munehisa Kamata > Signed-off-by: Anchal Agarwal > --- > drivers/xen/time.c | 29 ++++++++++++++++++++++++++++- > include/xen/xen-ops.h | 2 ++ > 2 files changed, 30 insertions(+), 1 deletion(-) > > diff --git a/drivers/xen/time.c b/drivers/xen/time.c > index 0968859c29d0..3560222cc0dd 100644 > --- a/drivers/xen/time.c > +++ b/drivers/xen/time.c > @@ -23,6 +23,9 @@ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_= runstate); > =20 > static DEFINE_PER_CPU(u64[4], old_runstate_time); > =20 > +static DEFINE_PER_CPU(u64, xen_prev_steal_clock); > +static DEFINE_PER_CPU(u64, xen_steal_clock_offset); Can you use old_runstate_time here? It is used to solve a similar problem for pv suspend, isn't it? -boris