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Sun, 13 Sep 2020 17:54:27 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 08DHnp8Y166603; Sun, 13 Sep 2020 17:52:26 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 33h7wjw3q1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 13 Sep 2020 17:52:26 +0000 Received: from abhmp0011.oracle.com (abhmp0011.oracle.com [141.146.116.17]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 08DHqGIo007221; Sun, 13 Sep 2020 17:52:16 GMT Received: from [10.74.86.192] (/10.74.86.192) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sun, 13 Sep 2020 17:52:16 +0000 Subject: Re: [PATCH v3 10/11] xen: Update sched clock offset to avoid system instability in hibernation 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: <238e837b8d4e17925801c4e85de17bdfca4ddd00.1598042152.git.anchalag@amazon.com> From: boris.ostrovsky@oracle.com Organization: Oracle Corporation Message-ID: <09bb5d50-ee13-133e-d5da-a342052e4271@oracle.com> Date: Sun, 13 Sep 2020 13:52:10 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.2.1 MIME-Version: 1.0 In-Reply-To: <238e837b8d4e17925801c4e85de17bdfca4ddd00.1598042152.git.anchalag@amazon.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9743 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 adultscore=0 bulkscore=0 phishscore=0 mlxlogscore=999 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009130163 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9743 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 spamscore=0 lowpriorityscore=0 malwarescore=0 mlxscore=0 bulkscore=0 suspectscore=0 clxscore=1015 mlxlogscore=999 adultscore=0 priorityscore=1501 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009130163 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/21/20 6:30 PM, Anchal Agarwal wrote: > Save/restore xen_sched_clock_offset in syscore suspend/resume during PM > hibernation. Commit '867cefb4cb1012: ("xen: Fix x86 sched_clock() interface > for xen")' fixes xen guest time handling during migration. A similar issue > is seen during PM hibernation when system runs CPU intensive workload. > Post resume pvclock resets the value to 0 however, xen sched_clock_offset > is never updated. System instability is seen during resume from hibernation > when system is under heavy CPU load. Since xen_sched_clock_offset is not > updated, system does not see the monotonic clock value and the scheduler > would then think that heavy CPU hog tasks need more time in CPU, causing > the system to freeze I don't think you need to explain why non-monotonic clocks are bad. (and, in fact, the same applies to commit message in patch 8) > > Signed-off-by: Anchal Agarwal > --- > arch/x86/xen/suspend.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c > index b12db6966af6..a62e08a11681 100644 > --- a/arch/x86/xen/suspend.c > +++ b/arch/x86/xen/suspend.c > @@ -98,8 +98,9 @@ static int xen_syscore_suspend(void) > return 0; > > gnttab_suspend(); > - > xen_manage_runstate_time(-1); > + xen_save_sched_clock_offset(); > + > xrfp.domid = DOMID_SELF; > xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT; > > @@ -120,6 +121,12 @@ static void xen_syscore_resume(void) > xen_hvm_map_shared_info(); > > pvclock_resume(); > + > + /* > + * Restore xen_sched_clock_offset during resume to maintain > + * monotonic clock value > + */ I'd drop this comment, we know what the call does. -boris > + xen_restore_sched_clock_offset(); > xen_manage_runstate_time(0); > gnttab_resume(); > }