| Message ID | 1509341179-8802-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 30/10/17 06:26, 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 > > 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. > > 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> > > --- > Changed since v1: > * relocate modification to xen_get_runstate_snapshot_cpu > > Changed since v2: > * accumulate runstate times before live migration > > Changed since v3: > * do not accumulate times in the case of guest checkpointing > > --- > drivers/xen/manage.c | 2 ++ > drivers/xen/time.c | 83 ++++++++++++++++++++++++++++++++++++++++++-- > include/xen/interface/vcpu.h | 2 ++ > include/xen/xen-ops.h | 1 + > 4 files changed, 86 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c > index c425d03..3dc085d 100644 > --- a/drivers/xen/manage.c > +++ b/drivers/xen/manage.c > @@ -72,6 +72,7 @@ static int xen_suspend(void *data) > } > > gnttab_suspend(); > + xen_accumulate_runstate_time(-1); > xen_arch_pre_suspend(); > > /* > @@ -84,6 +85,7 @@ static int xen_suspend(void *data) > : 0); > > xen_arch_post_suspend(si->cancelled); > + xen_accumulate_runstate_time(si->cancelled); > gnttab_resume(); > > if (!si->cancelled) { > diff --git a/drivers/xen/time.c b/drivers/xen/time.c > index ac5f23f..18e2b76 100644 > --- a/drivers/xen/time.c > +++ b/drivers/xen/time.c > @@ -19,6 +19,9 @@ > /* runstate info updated by Xen */ > static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate); > > +static DEFINE_PER_CPU(u64[RUNSTATE_max], old_runstate_time); > +static u64 **runstate_time_delta; > + > /* return an consistent snapshot of 64-bit time/counter value */ > static u64 get64(const u64 *p) > { > @@ -47,8 +50,8 @@ static u64 get64(const u64 *p) > return ret; > } > > -static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, > - unsigned int cpu) > +static void xen_get_runstate_snapshot_cpu_delta( > + struct vcpu_runstate_info *res, unsigned int cpu) > { > u64 state_time; > struct vcpu_runstate_info *state; > @@ -66,6 +69,82 @@ static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, > (state_time & XEN_RUNSTATE_UPDATE)); > } > > +static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, > + unsigned int cpu) > +{ > + int i; > + > + xen_get_runstate_snapshot_cpu_delta(res, cpu); > + > + for (i = 0; i < RUNSTATE_max; i++) > + res->time[i] += per_cpu(old_runstate_time, cpu)[i]; > +} > + > +void xen_accumulate_runstate_time(int action) > +{ > + struct vcpu_runstate_info state; > + int cpu, i; > + > + switch (action) { > + case -1: /* backup runstate time before suspend */ > + WARN_ON_ONCE(unlikely(runstate_time_delta)); > + > + runstate_time_delta = kcalloc(num_possible_cpus(), > + sizeof(*runstate_time_delta), > + GFP_KERNEL); You know the number of cpus, so you can just allocate an array of struct vcpu_runstate_info: struct vcpu_runstate_info *runstate_time_delta; kcalloc(num_possible_cpus(), sizeof(*runstate_time_delta), GFP_KERNEL); then ... > + if (unlikely(!runstate_time_delta)) { > + pr_alert("%s: failed to allocate runstate_time_delta\n", > + __func__); > + return; > + } > + > + for_each_possible_cpu(cpu) { > + runstate_time_delta[cpu] = kmalloc_array(RUNSTATE_max, > + sizeof(**runstate_time_delta), > + GFP_KERNEL); ... this allocation isn't needed any more. Juergen
Hi Dongli,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on xen-tip/linux-next]
[also build test ERROR on v4.14-rc7 next-20171018]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Dongli-Zhang/xen-time-do-not-decrease-steal-time-after-live-migration-on-xen/20171102-025719
base: https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git linux-next
config: arm64-allmodconfig (attached as .config)
compiler: aarch64-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=arm64
All errors (new ones prefixed by >>):
drivers/xen/time.c: In function 'xen_accumulate_runstate_time':
drivers/xen/time.c:92:25: error: implicit declaration of function 'kcalloc' [-Werror=implicit-function-declaration]
runstate_time_delta = kcalloc(num_possible_cpus(),
^~~~~~~
drivers/xen/time.c:92:23: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
runstate_time_delta = kcalloc(num_possible_cpus(),
^
>> drivers/xen/time.c:102:31: error: implicit declaration of function 'kmalloc_array' [-Werror=implicit-function-declaration]
runstate_time_delta[cpu] = kmalloc_array(RUNSTATE_max,
^~~~~~~~~~~~~
drivers/xen/time.c:102:29: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
runstate_time_delta[cpu] = kmalloc_array(RUNSTATE_max,
^
drivers/xen/time.c:141:5: error: implicit declaration of function 'kfree' [-Werror=implicit-function-declaration]
kfree(runstate_time_delta[cpu]);
^~~~~
cc1: some warnings being treated as errors
vim +/kmalloc_array +102 drivers/xen/time.c
82
83 void xen_accumulate_runstate_time(int action)
84 {
85 struct vcpu_runstate_info state;
86 int cpu, i;
87
88 switch (action) {
89 case -1: /* backup runstate time before suspend */
90 WARN_ON_ONCE(unlikely(runstate_time_delta));
91
> 92 runstate_time_delta = kcalloc(num_possible_cpus(),
93 sizeof(*runstate_time_delta),
94 GFP_KERNEL);
95 if (unlikely(!runstate_time_delta)) {
96 pr_alert("%s: failed to allocate runstate_time_delta\n",
97 __func__);
98 return;
99 }
100
101 for_each_possible_cpu(cpu) {
> 102 runstate_time_delta[cpu] = kmalloc_array(RUNSTATE_max,
103 sizeof(**runstate_time_delta),
104 GFP_KERNEL);
105 if (unlikely(!runstate_time_delta[cpu])) {
106 pr_alert("%s: failed to allocate runstate_time_delta[%d]\n",
107 __func__, cpu);
108 action = 0;
109 goto reclaim_mem;
110 }
111
112 xen_get_runstate_snapshot_cpu_delta(&state, cpu);
113 memcpy(runstate_time_delta[cpu],
114 state.time,
115 RUNSTATE_max * sizeof(**runstate_time_delta));
116 }
117 break;
118
119 case 0: /* backup runstate time after resume */
120 if (unlikely(!runstate_time_delta)) {
121 pr_alert("%s: cannot accumulate runstate time as runstate_time_delta is NULL\n",
122 __func__);
123 return;
124 }
125
126 for_each_possible_cpu(cpu) {
127 for (i = 0; i < RUNSTATE_max; i++)
128 per_cpu(old_runstate_time, cpu)[i] +=
129 runstate_time_delta[cpu][i];
130 }
131 break;
132
133 default: /* do not accumulate runstate time for checkpointing */
134 break;
135 }
136
137 reclaim_mem:
138 if (action != -1 && runstate_time_delta) {
139 for_each_possible_cpu(cpu) {
140 if (likely(runstate_time_delta[cpu]))
141 kfree(runstate_time_delta[cpu]);
142 }
143 kfree(runstate_time_delta);
144 runstate_time_delta = NULL;
145 }
146 }
147
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c index c425d03..3dc085d 100644 --- a/drivers/xen/manage.c +++ b/drivers/xen/manage.c @@ -72,6 +72,7 @@ static int xen_suspend(void *data) } gnttab_suspend(); + xen_accumulate_runstate_time(-1); xen_arch_pre_suspend(); /* @@ -84,6 +85,7 @@ static int xen_suspend(void *data) : 0); xen_arch_post_suspend(si->cancelled); + xen_accumulate_runstate_time(si->cancelled); gnttab_resume(); if (!si->cancelled) { diff --git a/drivers/xen/time.c b/drivers/xen/time.c index ac5f23f..18e2b76 100644 --- a/drivers/xen/time.c +++ b/drivers/xen/time.c @@ -19,6 +19,9 @@ /* runstate info updated by Xen */ static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate); +static DEFINE_PER_CPU(u64[RUNSTATE_max], old_runstate_time); +static u64 **runstate_time_delta; + /* return an consistent snapshot of 64-bit time/counter value */ static u64 get64(const u64 *p) { @@ -47,8 +50,8 @@ static u64 get64(const u64 *p) return ret; } -static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, - unsigned int cpu) +static void xen_get_runstate_snapshot_cpu_delta( + struct vcpu_runstate_info *res, unsigned int cpu) { u64 state_time; struct vcpu_runstate_info *state; @@ -66,6 +69,82 @@ static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, (state_time & XEN_RUNSTATE_UPDATE)); } +static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, + unsigned int cpu) +{ + int i; + + xen_get_runstate_snapshot_cpu_delta(res, cpu); + + for (i = 0; i < RUNSTATE_max; i++) + res->time[i] += per_cpu(old_runstate_time, cpu)[i]; +} + +void xen_accumulate_runstate_time(int action) +{ + struct vcpu_runstate_info state; + int cpu, i; + + switch (action) { + case -1: /* backup runstate time before suspend */ + WARN_ON_ONCE(unlikely(runstate_time_delta)); + + runstate_time_delta = kcalloc(num_possible_cpus(), + sizeof(*runstate_time_delta), + GFP_KERNEL); + if (unlikely(!runstate_time_delta)) { + pr_alert("%s: failed to allocate runstate_time_delta\n", + __func__); + return; + } + + for_each_possible_cpu(cpu) { + runstate_time_delta[cpu] = kmalloc_array(RUNSTATE_max, + sizeof(**runstate_time_delta), + GFP_KERNEL); + if (unlikely(!runstate_time_delta[cpu])) { + pr_alert("%s: failed to allocate runstate_time_delta[%d]\n", + __func__, cpu); + action = 0; + goto reclaim_mem; + } + + xen_get_runstate_snapshot_cpu_delta(&state, cpu); + memcpy(runstate_time_delta[cpu], + state.time, + RUNSTATE_max * sizeof(**runstate_time_delta)); + } + break; + + case 0: /* backup runstate time after resume */ + if (unlikely(!runstate_time_delta)) { + pr_alert("%s: cannot accumulate runstate time as runstate_time_delta is NULL\n", + __func__); + return; + } + + for_each_possible_cpu(cpu) { + for (i = 0; i < RUNSTATE_max; i++) + per_cpu(old_runstate_time, cpu)[i] += + runstate_time_delta[cpu][i]; + } + break; + + default: /* do not accumulate runstate time for checkpointing */ + break; + } + +reclaim_mem: + if (action != -1 && runstate_time_delta) { + for_each_possible_cpu(cpu) { + if (likely(runstate_time_delta[cpu])) + kfree(runstate_time_delta[cpu]); + } + kfree(runstate_time_delta); + runstate_time_delta = NULL; + } +} + /* * Runstate accounting */ diff --git a/include/xen/interface/vcpu.h b/include/xen/interface/vcpu.h index 98188c8..85e81ce 100644 --- a/include/xen/interface/vcpu.h +++ b/include/xen/interface/vcpu.h @@ -110,6 +110,8 @@ DEFINE_GUEST_HANDLE_STRUCT(vcpu_runstate_info); */ #define RUNSTATE_offline 3 +#define RUNSTATE_max 4 + /* * Register a shared memory area from which the guest may obtain its own * runstate information without needing to execute a hypercall. diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h index 218e6aa..b1f9ae9 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_accumulate_runstate_time(int action); void xen_get_runstate_snapshot(struct vcpu_runstate_info *res); u64 xen_steal_clock(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 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. 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> --- Changed since v1: * relocate modification to xen_get_runstate_snapshot_cpu Changed since v2: * accumulate runstate times before live migration Changed since v3: * do not accumulate times in the case of guest checkpointing --- drivers/xen/manage.c | 2 ++ drivers/xen/time.c | 83 ++++++++++++++++++++++++++++++++++++++++++-- include/xen/interface/vcpu.h | 2 ++ include/xen/xen-ops.h | 1 + 4 files changed, 86 insertions(+), 2 deletions(-)