| Message ID | cc35a710-c2ec-6c61-e30e-ee707798c5e9@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | sched/numa: introduce advanced numa statistic | expand |
On 11/26/19 5:50 PM, 王贇 wrote: > Since v1: > * thanks to Iurii for the better sentence > * thanks to Jonathan for the better format > > Add the description for 'cg_numa_stat', also a new doc to explain > the details on how to deal with the per-cgroup numa statistics. > > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Michal Koutný <mkoutny@suse.com> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Iurii Zaikin <yzaikin@google.com> > Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com> Hi, I have a few comments/corrections. Please see below. > --- > Documentation/admin-guide/cg-numa-stat.rst | 163 ++++++++++++++++++++++++ > Documentation/admin-guide/index.rst | 1 + > Documentation/admin-guide/kernel-parameters.txt | 4 + > Documentation/admin-guide/sysctl/kernel.rst | 9 ++ > 4 files changed, 177 insertions(+) > create mode 100644 Documentation/admin-guide/cg-numa-stat.rst > > diff --git a/Documentation/admin-guide/cg-numa-stat.rst b/Documentation/admin-guide/cg-numa-stat.rst > new file mode 100644 > index 000000000000..6f505f46fe00 > --- /dev/null > +++ b/Documentation/admin-guide/cg-numa-stat.rst > @@ -0,0 +1,163 @@ > +=============================== > +Per-cgroup NUMA statistics > +=============================== > + > +Background > +---------- > + > +On NUMA platforms, remote memory accessing always has a performance penalty, penalty. > +although we have NUMA balancing working hard to maximize the access locality, Although > +there are still situations it can't help. > + > +This could happen in modern production environment. When a large number of > +cgroups are used to classify and control resources, this creates a complex > +configuration for memory policy, CPUs and NUMA nodes. In such cases NUMA > +balancing could end up with the wrong memory policy or exhausted local NUMA > +node, which would lead to low percentage of local page accesses. > + > +We need to detect such cases, figure out which workloads from which cgroup > +has introduced the issues, then we get chance to do adjustment to avoid have > +performance degradation. > + > +However, there are no hardware counters for per-task local/remote accessing > +info, we don't know how many remote page accesses have occurred for a > +particular task. > + > +Statistics > +---------- > + > +Fortunately, we have NUMA Balancing which scans task's mapping and triggers PF > +periodically, gives us the opportunity to record per-task page accessing info. giving > + > +By "echo 1 > /proc/sys/kernel/cg_numa_stat" at runtime or adding boot parameter > +'cg_numa_stat', we will enable the accounting of per-cgroup numa statistics, NUMA > +the 'cpu.numa_stat' entry of CPU cgroup will show statistics:: > + > + locality -- execution time sectioned by task NUMA locality (in ms) > + exectime -- execution time sectioned by NUMA node (in ms) > + > +We define 'task NUMA locality' as:: > + > + nr_local_page_access * 100 / (nr_local_page_access + nr_remote_page_access) > + > +this per-task percentage value will be updated on the ticks for current task, This > +and the access counter will be updated on task's NUMA balancing PF, so only > +the pages which NUMA Balancing paid attention to will be accounted. > + > +On each tick, we acquire the locality of current task on that CPU, accumulating > +the ticks into the counter of corresponding locality region, tasks from the > +same group sharing the counters, becoming the group locality. > + > +Similarly, we acquire the NUMA node of current CPU where the current task is > +executing on, accumulating the ticks into the counter of corresponding node, > +becoming the per-cgroup node execution time. > + > +Note that the accounting is hierarchical, which means the numa statistics for NUMA > +a given group represents not only the workload of this group, but also the represent > +workloads of all it's descendants. its > + > +For example the 'cpu.numa_stat' show:: > + > + locality 39541 60962 36842 72519 118605 721778 946553 > + exectime 1220127 1458684 > + > +The locality is sectioned into 7 regions, approximately as:: > + > + 0-13% 14-27% 28-42% 43-56% 57-71% 72-85% 86-100% > + > +And exectime is sectioned into 2 nodes, 0 and 1 in this case. > + > +Thus we know the workload of this group and it's descendants have totally its > +executed 1220127ms on node_0 and 1458684ms on node_1, tasks with locality > +around 0~13% executed for 39541 ms, and tasks with locality around 87~100% > +executed for 946553 ms, which imply most of the memory access are local. > + > +Monitoring > +---------- > + > +By monitoring the increments of these statistics, we can easily know whether > +NUMA balancing is working well for a particular workload. > + > +For example we take a 5 secs sample period, and consider locality under 27% seconds > +is bad, then on each sampling we have:: > + > + region_bad = region_1 + region_2 > + region_all = region_1 + region_2 + ... + region_7 > + > +and we have the increments as:: > + > + region_bad_diff = region_bad - last_region_bad > + region_all_diff = region_all - last_region_all > + > +which finally become:: > + > + region_bad_percent = region_bad_diff * 100 / region_all_diff > + > +we can plot a line for region_bad_percent, when the line close to 0 things We > +are good, when getting close to 100% something is wrong, we can pick a proper > +watermark to trigger warning message. > + > +You may want to drop the data if the region_all is too small, which implies > +there are not many available pages for NUMA Balancing, ignoring would be fine > +since most likely the workload is insensitive to NUMA. > + > +Monitoring root group helps you control the overall situation, while you may > +also want to monitor all the leaf groups which contain the workloads, this > +helps to catch the mouse. > + > +The exectime could be useful when NUMA Balancing is disabled, or when locality > +becomes too small, for NUMA node X we have:: small. For > + > + exectime_X_diff = exectime_X - last_exectime_X > + exectime_all_diff = exectime_all - last_exectime_all > + > +try to put your workload into a memory cgroup which providing per-node memory Try provides > +consumption by 'memory.numa_stat' entry, then we could get:: > + > + memory_percent_X = memory_X * 100 / memory_all > + exectime_percent_X = exectime_X_diff * 100 / exectime_all_diff > + > +These two percentages are usually matched on each node, workload should execute > +mostly on the node contain most of it's memory, but it's not guaranteed. node that contains most of its > + > +The workload may only access a small part of it's memory, in such cases although its > +the majority of memory are remotely, locality could still be good. > + > +Thus to tell if things are fine or not depends on the understanding of system > +resource deployment, however, if you find node X got 100% memory percent but 0% > +exectime percent, definitely something is wrong. > + > +Troubleshooting > +--------------- > + > +After identifying which workload introduced the bad locality, check: > + > +1). Is the workload bound to a particular NUMA node? > +2). Has any NUMA node run out of resources? > + > +There are several ways to bind task's memory with a NUMA node, the strict way > +like the MPOL_BIND memory policy or 'cpuset.mems' will limiting the memory will limit > +node where to allocate pages, in this situation, admin should make sure the pages. In > +task is allowed to run on the CPUs of that NUMA node, and make sure there are > +available CPU resource there. > + > +There are also ways to bind task's CPU with a NUMA node, like 'cpuset.cpus' or > +sched_setaffinity() syscall, in this situation, NUMA Balancing help to migrate syscall. In > +pages into that node, admin should make sure there are available memory there. > + > +Admin could try rebind or unbind the NUMA node to erase the damage, make a try to > +change then observe the statistics see if things get better until the situation observe the statistics to see if > +is acceptable. > + > +Highlights > +---------- > + > +For some tasks, NUMA Balancing may found no necessary to scan pages, and > +locality could always be 0 or small number, don't pay attention to them > +since they most likely insensitive to NUMA. > + > +There are no accounting until the option turned on, so enable it in advance is no accounting until the option is turned on, > +if you want to have the whole history. > + > +We have per-task migfailed counter to tell how many page migration has been I can't find any occurrence of 'migfailed' in the entire kernel source tree. Maybe it is misspelled? > +failed for a particular task, you will find it in /proc/PID/sched entry. HTH.
Hi, Randy On 2019/11/27 下午12:58, Randy Dunlap wrote: > On 11/26/19 5:50 PM, 王贇 wrote: >> Since v1: >> * thanks to Iurii for the better sentence >> * thanks to Jonathan for the better format >> >> Add the description for 'cg_numa_stat', also a new doc to explain >> the details on how to deal with the per-cgroup numa statistics. >> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Michal Koutný <mkoutny@suse.com> >> Cc: Mel Gorman <mgorman@suse.de> >> Cc: Jonathan Corbet <corbet@lwn.net> >> Cc: Iurii Zaikin <yzaikin@google.com> >> Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com> > > Hi, > I have a few comments/corrections. Please see below. Thanks for the comments :-) will apply them all in next version. > >> --- >> Documentation/admin-guide/cg-numa-stat.rst | 163 [snip] >> +if you want to have the whole history. >> + >> +We have per-task migfailed counter to tell how many page migration has been > > I can't find any occurrence of 'migfailed' in the entire kernel source tree. > Maybe it is misspelled? This one is added by the secondary patch: [PATCH v2 2/3] sched/numa: expose per-task pages-migration-failure As suggested by Mel. Regards, Michael Wang > >> +failed for a particular task, you will find it in /proc/PID/sched entry. > > > HTH. >
diff --git a/Documentation/admin-guide/cg-numa-stat.rst b/Documentation/admin-guide/cg-numa-stat.rst new file mode 100644 index 000000000000..6f505f46fe00 --- /dev/null +++ b/Documentation/admin-guide/cg-numa-stat.rst @@ -0,0 +1,163 @@ +=============================== +Per-cgroup NUMA statistics +=============================== + +Background +---------- + +On NUMA platforms, remote memory accessing always has a performance penalty, +although we have NUMA balancing working hard to maximize the access locality, +there are still situations it can't help. + +This could happen in modern production environment. When a large number of +cgroups are used to classify and control resources, this creates a complex +configuration for memory policy, CPUs and NUMA nodes. In such cases NUMA +balancing could end up with the wrong memory policy or exhausted local NUMA +node, which would lead to low percentage of local page accesses. + +We need to detect such cases, figure out which workloads from which cgroup +has introduced the issues, then we get chance to do adjustment to avoid +performance degradation. + +However, there are no hardware counters for per-task local/remote accessing +info, we don't know how many remote page accesses have occurred for a +particular task. + +Statistics +---------- + +Fortunately, we have NUMA Balancing which scans task's mapping and triggers PF +periodically, gives us the opportunity to record per-task page accessing info. + +By "echo 1 > /proc/sys/kernel/cg_numa_stat" at runtime or adding boot parameter +'cg_numa_stat', we will enable the accounting of per-cgroup numa statistics, +the 'cpu.numa_stat' entry of CPU cgroup will show statistics:: + + locality -- execution time sectioned by task NUMA locality (in ms) + exectime -- execution time sectioned by NUMA node (in ms) + +We define 'task NUMA locality' as:: + + nr_local_page_access * 100 / (nr_local_page_access + nr_remote_page_access) + +this per-task percentage value will be updated on the ticks for current task, +and the access counter will be updated on task's NUMA balancing PF, so only +the pages which NUMA Balancing paid attention to will be accounted. + +On each tick, we acquire the locality of current task on that CPU, accumulating +the ticks into the counter of corresponding locality region, tasks from the +same group sharing the counters, becoming the group locality. + +Similarly, we acquire the NUMA node of current CPU where the current task is +executing on, accumulating the ticks into the counter of corresponding node, +becoming the per-cgroup node execution time. + +Note that the accounting is hierarchical, which means the numa statistics for +a given group represents not only the workload of this group, but also the +workloads of all it's descendants. + +For example the 'cpu.numa_stat' show:: + + locality 39541 60962 36842 72519 118605 721778 946553 + exectime 1220127 1458684 + +The locality is sectioned into 7 regions, approximately as:: + + 0-13% 14-27% 28-42% 43-56% 57-71% 72-85% 86-100% + +And exectime is sectioned into 2 nodes, 0 and 1 in this case. + +Thus we know the workload of this group and it's descendants have totally +executed 1220127ms on node_0 and 1458684ms on node_1, tasks with locality +around 0~13% executed for 39541 ms, and tasks with locality around 87~100% +executed for 946553 ms, which imply most of the memory access are local. + +Monitoring +---------- + +By monitoring the increments of these statistics, we can easily know whether +NUMA balancing is working well for a particular workload. + +For example we take a 5 secs sample period, and consider locality under 27% +is bad, then on each sampling we have:: + + region_bad = region_1 + region_2 + region_all = region_1 + region_2 + ... + region_7 + +and we have the increments as:: + + region_bad_diff = region_bad - last_region_bad + region_all_diff = region_all - last_region_all + +which finally become:: + + region_bad_percent = region_bad_diff * 100 / region_all_diff + +we can plot a line for region_bad_percent, when the line close to 0 things +are good, when getting close to 100% something is wrong, we can pick a proper +watermark to trigger warning message. + +You may want to drop the data if the region_all is too small, which implies +there are not many available pages for NUMA Balancing, ignoring would be fine +since most likely the workload is insensitive to NUMA. + +Monitoring root group helps you control the overall situation, while you may +also want to monitor all the leaf groups which contain the workloads, this +helps to catch the mouse. + +The exectime could be useful when NUMA Balancing is disabled, or when locality +becomes too small, for NUMA node X we have:: + + exectime_X_diff = exectime_X - last_exectime_X + exectime_all_diff = exectime_all - last_exectime_all + +try to put your workload into a memory cgroup which providing per-node memory +consumption by 'memory.numa_stat' entry, then we could get:: + + memory_percent_X = memory_X * 100 / memory_all + exectime_percent_X = exectime_X_diff * 100 / exectime_all_diff + +These two percentages are usually matched on each node, workload should execute +mostly on the node contain most of it's memory, but it's not guaranteed. + +The workload may only access a small part of it's memory, in such cases although +the majority of memory are remotely, locality could still be good. + +Thus to tell if things are fine or not depends on the understanding of system +resource deployment, however, if you find node X got 100% memory percent but 0% +exectime percent, definitely something is wrong. + +Troubleshooting +--------------- + +After identifying which workload introduced the bad locality, check: + +1). Is the workload bound to a particular NUMA node? +2). Has any NUMA node run out of resources? + +There are several ways to bind task's memory with a NUMA node, the strict way +like the MPOL_BIND memory policy or 'cpuset.mems' will limiting the memory +node where to allocate pages, in this situation, admin should make sure the +task is allowed to run on the CPUs of that NUMA node, and make sure there are +available CPU resource there. + +There are also ways to bind task's CPU with a NUMA node, like 'cpuset.cpus' or +sched_setaffinity() syscall, in this situation, NUMA Balancing help to migrate +pages into that node, admin should make sure there are available memory there. + +Admin could try rebind or unbind the NUMA node to erase the damage, make a +change then observe the statistics see if things get better until the situation +is acceptable. + +Highlights +---------- + +For some tasks, NUMA Balancing may found no necessary to scan pages, and +locality could always be 0 or small number, don't pay attention to them +since they most likely insensitive to NUMA. + +There are no accounting until the option turned on, so enable it in advance +if you want to have the whole history. + +We have per-task migfailed counter to tell how many page migration has been +failed for a particular task, you will find it in /proc/PID/sched entry. diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index 4405b7485312..c75a3fdfcd94 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -112,6 +112,7 @@ configure specific aspects of kernel behavior to your liking. video-output wimax/index xfs + cg-numa-stat .. only:: subproject and html diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 0945611b3877..674c1a4bae14 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3227,6 +3227,10 @@ numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. Allowed values are enable and disable + cg_numa_atat [KNL] Enable advanced per-cgroup numa statistics. + Useful to debug NUMA efficiency problems when there are + lots of per-cgroup workloads. + numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 'node', 'default' can be specified This can be set from sysctl after boot. diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index 7e203b3ed331..918a26d2bd77 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -572,6 +572,15 @@ rate for each task. numa_balancing_scan_size_mb is how many megabytes worth of pages are scanned for a given scan. +cg_numa_stat: +============= + +Enables/disables advanced per-cgroup NUMA statistic. + +0: disabled (default). +1: enabled. + +Check Documentation/admin-guide/cg-numa-stat.rst for details. osrelease, ostype & version: ============================
Since v1: * thanks to Iurii for the better sentence * thanks to Jonathan for the better format Add the description for 'cg_numa_stat', also a new doc to explain the details on how to deal with the per-cgroup numa statistics. Cc: Peter Zijlstra <peterz@infradead.org> Cc: Michal Koutný <mkoutny@suse.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Iurii Zaikin <yzaikin@google.com> Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com> --- Documentation/admin-guide/cg-numa-stat.rst | 163 ++++++++++++++++++++++++ Documentation/admin-guide/index.rst | 1 + Documentation/admin-guide/kernel-parameters.txt | 4 + Documentation/admin-guide/sysctl/kernel.rst | 9 ++ 4 files changed, 177 insertions(+) create mode 100644 Documentation/admin-guide/cg-numa-stat.rst