| Message ID | 1508400179-10204-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 10/19/2017 04:02 AM, Dongli Zhang wrote: > 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 > > The code in this patch is borrowed from do_stolen_accounting() which has > already been removed from linux source code since commit ecb23dc6f2ef > ("xen: add steal_clock support on x86"). The core idea of both > do_stolen_accounting() and this patch is to avoid accounting new steal > clock if it is smaller than previous old steal clock. > > 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. > > 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> > --- > drivers/xen/time.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/drivers/xen/time.c b/drivers/xen/time.c > index ac5f23f..2b3a996 100644 > --- a/drivers/xen/time.c > +++ b/drivers/xen/time.c > @@ -19,6 +19,8 @@ > /* runstate info updated by Xen */ > static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate); > > +static DEFINE_PER_CPU(u64, xen_old_steal); > + > /* return an consistent snapshot of 64-bit time/counter value */ > static u64 get64(const u64 *p) > { > @@ -83,9 +85,20 @@ bool xen_vcpu_stolen(int vcpu) > u64 xen_steal_clock(int cpu) > { > struct vcpu_runstate_info state; > + u64 xen_new_steal; > + s64 steal_delta; > > xen_get_runstate_snapshot_cpu(&state, cpu); > - return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; > + xen_new_steal = state.time[RUNSTATE_runnable] > + + state.time[RUNSTATE_offline]; > + steal_delta = xen_new_steal - per_cpu(xen_old_steal, cpu); > + > + if (steal_delta < 0) > + xen_new_steal = per_cpu(xen_old_steal, cpu); > + else > + per_cpu(xen_old_steal, cpu) = xen_new_steal; > + > + return xen_new_steal; > } > > void xen_setup_runstate_info(int cpu) Can we stash state.time[] during suspend and then add stashed values inside xen_get_runstate_snapshot_cpu()? This will make xen_steal_clock() simpler. -boris
diff --git a/drivers/xen/time.c b/drivers/xen/time.c index ac5f23f..2b3a996 100644 --- a/drivers/xen/time.c +++ b/drivers/xen/time.c @@ -19,6 +19,8 @@ /* runstate info updated by Xen */ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate); +static DEFINE_PER_CPU(u64, xen_old_steal); + /* return an consistent snapshot of 64-bit time/counter value */ static u64 get64(const u64 *p) { @@ -83,9 +85,20 @@ bool xen_vcpu_stolen(int vcpu) u64 xen_steal_clock(int cpu) { struct vcpu_runstate_info state; + u64 xen_new_steal; + s64 steal_delta; xen_get_runstate_snapshot_cpu(&state, cpu); - return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; + xen_new_steal = state.time[RUNSTATE_runnable] + + state.time[RUNSTATE_offline]; + steal_delta = xen_new_steal - per_cpu(xen_old_steal, cpu); + + if (steal_delta < 0) + xen_new_steal = per_cpu(xen_old_steal, cpu); + else + per_cpu(xen_old_steal, cpu) = xen_new_steal; + + return xen_new_steal; } void xen_setup_runstate_info(int cpu)
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 The code in this patch is borrowed from do_stolen_accounting() which has already been removed from linux source code since commit ecb23dc6f2ef ("xen: add steal_clock support on x86"). The core idea of both do_stolen_accounting() and this patch is to avoid accounting new steal clock if it is smaller than previous old steal clock. 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. 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> --- drivers/xen/time.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)