Re: [Xen-devel] [PATCH v5 1/1] xen/time: do not decrease steal time after live migration on xen
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/20171102-011408 base: https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git linux-next config: arm64-defconfig (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 error/warnings (new ones prefixed by >>): drivers//xen/time.c: In function 'xen_accumulate_runstate_time': >> drivers//xen/time.c:92:20: error: implicit declaration of function 'kcalloc' >> [-Werror=implicit-function-declaration] runstate_delta = kcalloc(num_possible_cpus(), ^~~ >> drivers//xen/time.c:92:18: warning: assignment makes pointer from integer >> without a cast [-Wint-conversion] runstate_delta = kcalloc(num_possible_cpus(), ^ >> drivers//xen/time.c:128:3: error: implicit declaration of function 'kfree' >> [-Werror=implicit-function-declaration] kfree(runstate_delta); ^ cc1: some warnings being treated as errors vim +/kcalloc +92 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_delta)); 91 > 92 runstate_delta = kcalloc(num_possible_cpus(), 93 sizeof(*runstate_delta), 94 GFP_KERNEL); 95 if (unlikely(!runstate_delta)) { 96 pr_alert("%s: failed to allocate runstate_delta\n", 97 __func__); 98 return; 99 } 100 101 for_each_possible_cpu(cpu) { 102 xen_get_runstate_snapshot_cpu_delta(, cpu); 103 memcpy(runstate_delta[cpu].time, state.time, 104RUNSTATE_max * sizeof(*runstate_delta[cpu].time)); 105 } 106 107 break; 108 109 case 0: /* backup runstate time after resume */ 110 if (unlikely(!runstate_delta)) { 111 pr_alert("%s: cannot accumulate runstate time as runstate_delta is NULL\n", 112 __func__); 113 return; 114 } 115 116 for_each_possible_cpu(cpu) { 117 for (i = 0; i < RUNSTATE_max; i++) 118 per_cpu(old_runstate_time, cpu)[i] += 119 runstate_delta[cpu].time[i]; 120 } 121 break; 122 123 default: /* do not accumulate runstate time for checkpointing */ 124 break; 125 } 126 127 if (action != -1 && runstate_delta) { > 128 kfree(runstate_delta); 129 runstate_delta = NULL; 130 } 131 } 132 --- 0-DAY kernel test infrastructureOpen Source Technology Center https://lists.01.org/pipermail/kbuild-all Intel Corporation .config.gz Description: application/gzip ___ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH v5 1/1] xen/time: do not decrease steal time after live migration on xen
On 10/30/2017 11:13 PM, Dongli Zhang wrote: Hi Boris, On 10/31/2017 08:58 AM, Boris Ostrovsky wrote: On 10/30/2017 08:14 PM, Dongli Zhang wrote: Hi Boris, On 10/30/2017 09:34 PM, Boris Ostrovsky wrote: On 10/30/2017 04:03 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 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--- 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 Changed since v4: * allocate array of vcpu_runstate_info to reduce number of memory allocation --- drivers/xen/manage.c | 2 ++ drivers/xen/time.c | 68 ++-- include/xen/interface/vcpu.h | 2 ++ include/xen/xen-ops.h| 1 + 4 files changed, 71 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); I am not convinced that the comment above HYPERVISOR_suspend() is correct. The call can return an error code and so if it returns -EPERM (which AFAICS it can't now but might in the future) then xen_accumulate_runstate_time() will do wrong thing. I would split xen_accumulate_runstate_time() into two functions to avoid the -EPERM issue, as one is for saving and another is for accumulation, respectively. Otherwise, can you use xen_accumulate_runstate_time(2) for saving before suspend and xen_accumulate_runstate_time(si->cancelled) after resume? I'd probably just say something like si->cancelled = HYPERVISOR_suspend() ? 1 : 0; As the call of HYPERVISOR_suspend() takes 3 lines, I would make it as below and I think gcc would optimize it. - /* -* This hypercall returns 1 if suspend was cancelled -* or the domain was merely checkpointed, and 0 if it -* is resuming in a new domain. -*/ si->cancelled = HYPERVISOR_suspend(xen_pv_domain() ? virt_to_gfn(xen_start_info) : 0); + si->cancelled = si->cancelled ? 1 : 0; Or xen_manage_runstate_time(si->cancelled ? 1 : 0) --- that way you preserve si->cancelled if anyone cares later (which at the moment nooone does) Either way I think is fine. and keep xen_accumulate_runstate_time() as is (maybe rename it to xen_manage_runstate_time()). And also remove the comment above the hypercall as it is incorrect (but please mention the reason in the commit message) gnttab_resume(); if (!si->cancelled) { diff --git a/drivers/xen/time.c b/drivers/xen/time.c index ac5f23f..cf3afb9 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 struct vcpu_runstate_info *runstate_delta; I'd move this inside
Re: [Xen-devel] [PATCH v5 1/1] xen/time: do not decrease steal time after live migration on xen
Hi Boris, On 10/31/2017 08:58 AM, Boris Ostrovsky wrote: > > > On 10/30/2017 08:14 PM, Dongli Zhang wrote: >> Hi Boris, >> >> On 10/30/2017 09:34 PM, Boris Ostrovsky wrote: >>> On 10/30/2017 04:03 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 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--- 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 Changed since v4: * allocate array of vcpu_runstate_info to reduce number of memory allocation --- drivers/xen/manage.c | 2 ++ drivers/xen/time.c | 68 ++-- include/xen/interface/vcpu.h | 2 ++ include/xen/xen-ops.h| 1 + 4 files changed, 71 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); >>> >>> I am not convinced that the comment above HYPERVISOR_suspend() is >>> correct. The call can return an error code and so if it returns -EPERM >>> (which AFAICS it can't now but might in the future) then >>> xen_accumulate_runstate_time() will do wrong thing. >> >> I would split xen_accumulate_runstate_time() into two functions to avoid the >> -EPERM issue, as one is for saving and another is for accumulation, >> respectively. >> >> Otherwise, can you use xen_accumulate_runstate_time(2) for saving before >> suspend >> and xen_accumulate_runstate_time(si->cancelled) after resume? > > > I'd probably just say something like > > si->cancelled = HYPERVISOR_suspend() ? 1 : 0; As the call of HYPERVISOR_suspend() takes 3 lines, I would make it as below and I think gcc would optimize it. - /* -* This hypercall returns 1 if suspend was cancelled -* or the domain was merely checkpointed, and 0 if it -* is resuming in a new domain. -*/ si->cancelled = HYPERVISOR_suspend(xen_pv_domain() ? virt_to_gfn(xen_start_info) : 0); + si->cancelled = si->cancelled ? 1 : 0; > > and keep xen_accumulate_runstate_time() as is (maybe rename it to > xen_manage_runstate_time()). And also remove the comment above the hypercall > as > it is incorrect (but please mention the reason in the commit message) > >> >>> >>> gnttab_resume(); if (!si->cancelled) { diff --git a/drivers/xen/time.c b/drivers/xen/time.c index ac5f23f..cf3afb9 100644 --- a/drivers/xen/time.c +++ b/drivers/xen/time.c @@ -19,6 +19,9 @@ /* runstate
Re: [Xen-devel] [PATCH v5 1/1] xen/time: do not decrease steal time after live migration on xen
On 10/30/2017 08:14 PM, Dongli Zhang wrote: Hi Boris, On 10/30/2017 09:34 PM, Boris Ostrovsky wrote: On 10/30/2017 04:03 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 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--- 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 Changed since v4: * allocate array of vcpu_runstate_info to reduce number of memory allocation --- drivers/xen/manage.c | 2 ++ drivers/xen/time.c | 68 ++-- include/xen/interface/vcpu.h | 2 ++ include/xen/xen-ops.h| 1 + 4 files changed, 71 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); I am not convinced that the comment above HYPERVISOR_suspend() is correct. The call can return an error code and so if it returns -EPERM (which AFAICS it can't now but might in the future) then xen_accumulate_runstate_time() will do wrong thing. I would split xen_accumulate_runstate_time() into two functions to avoid the -EPERM issue, as one is for saving and another is for accumulation, respectively. Otherwise, can you use xen_accumulate_runstate_time(2) for saving before suspend and xen_accumulate_runstate_time(si->cancelled) after resume? I'd probably just say something like si->cancelled = HYPERVISOR_suspend() ? 1 : 0; and keep xen_accumulate_runstate_time() as is (maybe rename it to xen_manage_runstate_time()). And also remove the comment above the hypercall as it is incorrect (but please mention the reason in the commit message) gnttab_resume(); if (!si->cancelled) { diff --git a/drivers/xen/time.c b/drivers/xen/time.c index ac5f23f..cf3afb9 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 struct vcpu_runstate_info *runstate_delta; I'd move this inside xen_accumulate_runstate_time() since that's the If we split xen_accumulate_runstate_time() into two functions, we would leave runstate_delta as global static. only function that uses it. And why does it need to be vcpu_runstate_info and not u64[4]? This was suggested by Juergen to avoid the allocation and reclaim of the second dimensional array as in v4 of this patch? Or would you like to allocate sizeof(u64[4]) * num_possible_cpus() and emulate the 2d array with this 1d array and move the pointer forward sizeof(u64[4]) in each iteration? I was thinking of u64 **runstate_delta = (u64 **)kmalloc(sizeof(xen_runstate.time) * num_possible_cpus()) and then you should be able to access runstate_delta[cpu][RUNSTATE_*]. + /* return an consistent snapshot of 64-bit time/counter value
Re: [Xen-devel] [PATCH v5 1/1] xen/time: do not decrease steal time after live migration on xen
Hi Boris, On 10/30/2017 09:34 PM, Boris Ostrovsky wrote: > On 10/30/2017 04:03 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 >> >> 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>> >> --- >> 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 >> >> Changed since v4: >> * allocate array of vcpu_runstate_info to reduce number of memory >> allocation >> >> --- >> drivers/xen/manage.c | 2 ++ >> drivers/xen/time.c | 68 >> ++-- >> include/xen/interface/vcpu.h | 2 ++ >> include/xen/xen-ops.h| 1 + >> 4 files changed, 71 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); > > I am not convinced that the comment above HYPERVISOR_suspend() is > correct. The call can return an error code and so if it returns -EPERM > (which AFAICS it can't now but might in the future) then > xen_accumulate_runstate_time() will do wrong thing. I would split xen_accumulate_runstate_time() into two functions to avoid the -EPERM issue, as one is for saving and another is for accumulation, respectively. Otherwise, can you use xen_accumulate_runstate_time(2) for saving before suspend and xen_accumulate_runstate_time(si->cancelled) after resume? > > >> gnttab_resume(); >> >> if (!si->cancelled) { >> diff --git a/drivers/xen/time.c b/drivers/xen/time.c >> index ac5f23f..cf3afb9 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 struct vcpu_runstate_info *runstate_delta; > > I'd move this inside xen_accumulate_runstate_time() since that's the If we split xen_accumulate_runstate_time() into two functions, we would leave runstate_delta as global static. > only function that uses it. And why does it need to be > vcpu_runstate_info and not u64[4]? This was suggested by Juergen to avoid the allocation and reclaim of the second dimensional array as in v4 of this patch? Or would you like to allocate sizeof(u64[4]) * num_possible_cpus() and emulate the 2d array with this 1d array and move the pointer forward sizeof(u64[4]) in each iteration? > >> + >> /* 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
Re: [Xen-devel] [PATCH v5 1/1] xen/time: do not decrease steal time after live migration on xen
On 10/30/2017 04:03 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 > > 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> > --- > 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 > > Changed since v4: > * allocate array of vcpu_runstate_info to reduce number of memory allocation > > --- > drivers/xen/manage.c | 2 ++ > drivers/xen/time.c | 68 > ++-- > include/xen/interface/vcpu.h | 2 ++ > include/xen/xen-ops.h| 1 + > 4 files changed, 71 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); I am not convinced that the comment above HYPERVISOR_suspend() is correct. The call can return an error code and so if it returns -EPERM (which AFAICS it can't now but might in the future) then xen_accumulate_runstate_time() will do wrong thing. > gnttab_resume(); > > if (!si->cancelled) { > diff --git a/drivers/xen/time.c b/drivers/xen/time.c > index ac5f23f..cf3afb9 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 struct vcpu_runstate_info *runstate_delta; I'd move this inside xen_accumulate_runstate_time() since that's the only function that uses it. And why does it need to be vcpu_runstate_info and not u64[4]? > + > /* 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 +69,67 @@ 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 */ > +
[Xen-devel] [PATCH v5 1/1] 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. 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--- 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 Changed since v4: * allocate array of vcpu_runstate_info to reduce number of memory allocation --- drivers/xen/manage.c | 2 ++ drivers/xen/time.c | 68 ++-- include/xen/interface/vcpu.h | 2 ++ include/xen/xen-ops.h| 1 + 4 files changed, 71 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..cf3afb9 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 struct vcpu_runstate_info *runstate_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 +69,67 @@ 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_delta)); + + runstate_delta = kcalloc(num_possible_cpus(), +sizeof(*runstate_delta), +GFP_KERNEL); + if (unlikely(!runstate_delta)) { + pr_alert("%s: failed to allocate runstate_delta\n", + __func__); + return; + } + + for_each_possible_cpu(cpu) { + xen_get_runstate_snapshot_cpu_delta(, cpu); + memcpy(runstate_delta[cpu].time, state.time, +