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authorDongli Zhang <dongli.zhang@oracle.com>2017-11-01 04:46:33 +0300
committerBoris Ostrovsky <boris.ostrovsky@oracle.com>2017-11-02 23:49:41 +0300
commit5e25f5db6abb96ca8ee2aaedcb863daa6dfcc07a (patch)
tree93d43c7dd843842ebb6fdef59d2fc6dfaa32a5e4 /include/xen
parent6f0e8bf16730a36ff6773802d8c8df56d10e60cd (diff)
downloadlinux-5e25f5db6abb96ca8ee2aaedcb863daa6dfcc07a.tar.xz
xen/time: do not decrease steal time after live migration on xen
After guest live migration on xen, steal time in /proc/stat (cpustat[CPUTIME_STEAL]) might decrease because steal returned by xen_steal_lock() might be less than this_rq()->prev_steal_time which is derived from previous return value of xen_steal_clock(). For instance, steal time of each vcpu is 335 before live migration. cpu 198 0 368 200064 1962 0 0 1340 0 0 cpu0 38 0 81 50063 492 0 0 335 0 0 cpu1 65 0 97 49763 634 0 0 335 0 0 cpu2 38 0 81 50098 462 0 0 335 0 0 cpu3 56 0 107 50138 374 0 0 335 0 0 After live migration, steal time is reduced to 312. cpu 200 0 370 200330 1971 0 0 1248 0 0 cpu0 38 0 82 50123 500 0 0 312 0 0 cpu1 65 0 97 49832 634 0 0 312 0 0 cpu2 39 0 82 50167 462 0 0 312 0 0 cpu3 56 0 107 50207 374 0 0 312 0 0 Since runstate times are cumulative and cleared during xen live migration by xen hypervisor, the idea of this patch is to accumulate runstate times to global percpu variables before live migration suspend. Once guest VM is resumed, xen_get_runstate_snapshot_cpu() would always return the sum of new runstate times and previously accumulated times stored in global percpu variables. Comment above HYPERVISOR_suspend() has been removed as it is inaccurate: the call can return an error code (e.g., possibly -EPERM in the future). Similar and more severe issue would impact prior linux 4.8-4.10 as discussed by Michael Las at https://0xstubs.org/debugging-a-flaky-cpu-steal-time-counter-on-a-paravirtualized-xen-guest, which would overflow steal time and lead to 100% st usage in top command for linux 4.8-4.10. A backport of this patch would fix that issue. [boris: added linux/slab.h to driver/xen/time.c, slightly reformatted commit message] References: https://0xstubs.org/debugging-a-flaky-cpu-steal-time-counter-on-a-paravirtualized-xen-guest Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Diffstat (limited to 'include/xen')
-rw-r--r--include/xen/xen-ops.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 218e6aae5433..09072271f122 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -32,6 +32,7 @@ void xen_resume_notifier_unregister(struct notifier_block *nb);
bool xen_vcpu_stolen(int vcpu);
void xen_setup_runstate_info(int cpu);
void xen_time_setup_guest(void);
+void xen_manage_runstate_time(int action);
void xen_get_runstate_snapshot(struct vcpu_runstate_info *res);
u64 xen_steal_clock(int cpu);