On 5/19/20 7:28 PM, Anchal Agarwal wrote: > From: Munehisa Kamata <kamatam@xxxxxxxxxx> > > 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 in > 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 <kamatam@xxxxxxxxxx> > Signed-off-by: Anchal Agarwal <anchalag@xxxxxxxxxx> > --- > 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); > > static DEFINE_PER_CPU(u64[4], old_runstate_time); > > +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
