From: 王贇 <yun.wang@linux.alibaba.com> To: "Ingo Molnar" <mingo@redhat.com>, "Peter Zijlstra" <peterz@infradead.org>, "Juri Lelli" <juri.lelli@redhat.com>, "Vincent Guittot" <vincent.guittot@linaro.org>, "Dietmar Eggemann" <dietmar.eggemann@arm.com>, "Steven Rostedt" <rostedt@goodmis.org>, "Ben Segall" <bsegall@google.com>, "Mel Gorman" <mgorman@suse.de>, "Luis Chamberlain" <mcgrof@kernel.org>, "Kees Cook" <keescook@chromium.org>, "Iurii Zaikin" <yzaikin@google.com>, "Michal Koutný" <mkoutny@suse.com>, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, "Paul E. McKenney" <paulmck@linux.ibm.com>, "Randy Dunlap" <rdunlap@infradead.org>, "Jonathan Corbet" <corbet@lwn.net> Subject: [PATCH v5 2/2] sched/numa: documentation for per-cgroup numa, statistics Date: Thu, 5 Dec 2019 14:54:47 +0800 Message-ID: <b4e303ab-9692-8fd2-fa5f-1b07248d07b6@linux.alibaba.com> (raw) In-Reply-To: <443641e7-f968-0954-5ff6-3b7e7fed0e83@linux.alibaba.com> Add the description for 'numa_locality', 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> Cc: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com> --- Documentation/admin-guide/cg-numa-stat.rst | 178 ++++++++++++++++++++++++ Documentation/admin-guide/index.rst | 1 + Documentation/admin-guide/kernel-parameters.txt | 4 + Documentation/admin-guide/sysctl/kernel.rst | 9 ++ init/Kconfig | 2 + 5 files changed, 194 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..30ebe5d6404f --- /dev/null +++ b/Documentation/admin-guide/cg-numa-stat.rst @@ -0,0 +1,178 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============================== +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 +have 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. + +NUMA Locality +------------- + +Fortunately, we have NUMA Balancing which scans task's mapping and triggers +page fault periodically, giving us the opportunity to record per-task page +accessing info, when the CPU fall into PF is from the same node of pages, we +consider task as doing local page accessing, otherwise the remote page +accessing, we call these two counter the locality info. + +On each tick, we acquire the locality info of current task on that CPU, update +the increments into its cgroup, becoming the group locality info. + +By "echo 1 > /proc/sys/kernel/numa_locality" at runtime or adding boot parameter +'numa_locality', we will enable the accounting of per-cgroup NUMA locality info, +the 'cpu.numa_stat' entry of CPU cgroup will show statistics:: + + page_access local=NR_LOCAL_PAGE_ACCESS remote=NR_REMOTE_PAGE_ACCESS + +We define 'NUMA locality' as:: + + NR_LOCAL_PAGE_ACCESS * 100 / (NR_LOCAL_PAGE_ACCESS + NR_REMOTE_PAGE_ACCESS) + +This per-cgroup percentage number helps to represent the NUMA Balancing behavior. + +Note that the accounting is hierarchical, which means the NUMA locality info for +a given group represent not only the workload of this group, but also the +workloads of all its descendants. + +For example the 'cpu.numa_stat' shows:: + + page_access local=129909383 remote=18265810 + +The NUMA locality calculated as:: + + 129909383 * 100 / (129909383 + 18265810) = 87.67 + +Thus we know the workload of this group and its descendants have totally done +129909383 times of local page accessing and 18265810 times of remotes, locality +is 87.67% which imply most of the memory access are local. + +NUMA Consumption +---------------- + +There are also other cgroup entry help us to estimate NUMA efficiency, which is +'cpuacct.usage_percpu' and 'memory.numa_stat'. + +By reading 'cpuacct.usage_percpu' we will get per-cpu runtime (in nanoseconds) +info (in hierarchy) as:: + + CPU_0_RUNTIME CPU_1_RUNTIME CPU_2_RUNTIME ... CPU_X_RUNTIME + +Combined with the info from:: + + cat /sys/devices/system/node/nodeX/cpulist + +We would be able to accumulate the runtime of CPUs into NUMA nodes, to get the +per-cgroup node runtime info. + +By reading 'memory.numa_stat' we will get per-cgroup node memory consumption +info as:: + + total=TOTAL_MEM N0=MEM_ON_NODE0 N1=MEM_ON_NODE1 ... NX=MEM_ON_NODEX + +Together we call these the per-cgroup NUMA consumption info, tell us how many +resources a particular workload has consumed, on a particular NUMA node. + +Monitoring +---------- + +By monitoring the increments of locality info, we can easily know whether NUMA +Balancing is working well for a particular workload. + +For example we take a 5 seconds sample period, then on each sampling we have:: + + local_diff = last_nr_local_page_access - nr_local_page_access + remote_diff = last_nr_remote_page_access - nr_remote_page_access + +and we get the locality in this period as:: + + locality = local_diff * 100 / (local_diff + remote_diff) + +We can plot a line for locality, when the line close to 100% things are good, +when getting close to 0% something is wrong, we can pick a proper watermark to +trigger warning message. + +You may want to drop the data if the local/remote_diff is too small, which +implies there are not many available pages for NUMA Balancing to scan, ignoring +would be fine since most likely the workload is insensitive to NUMA, or the +memory topology is already good enough. + +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. + +Try to put your workload into also the cpuacct & memory cgroup, when NUMA +Balancing is disabled or locality becomes too small, we may want to monitor +the per-node runtime & memory info to see if the node consumption meet the +requirements. + +For NUMA node X on each sampling we have:: + + runtime_X_diff = runtime_X - last_runtime_X + runtime_all_diff = runtime_all - last_runtime_all + + runtime_percent_X = runtime_X_diff * 100 / runtime_all_diff + memory_percent_X = memory_X * 100 / memory_all + +These two percentages are usually matched on each node, workload should execute +mostly on the node that contains most of its memory, but it's not guaranteed. + +The workload may only access a small part of its 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% +runtime 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 limit 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 to rebind or unbind the NUMA node to erase the damage, make a +change then observe the statistics to see if things get better until the +situation is acceptable. + +Highlights +---------- + +For some tasks, NUMA Balancing may be found to be unnecessary 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 is no accounting until the option is 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..9d9e57d19af3 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 + numa_locality [KNL] Enable per-cgroup numa locality info. + 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..efa995e757fd 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. +numa_locality: +============= + +Enables/disables per-cgroup NUMA locality info. + +0: disabled (default). +1: enabled. + +Check Documentation/admin-guide/cg-numa-stat.rst for details. osrelease, ostype & version: ============================ diff --git a/init/Kconfig b/init/Kconfig index c614ba6bdcc2..3538fdd73387 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -825,6 +825,8 @@ config CGROUP_NUMA_LOCALITY This option enables the collection of per-cgroup NUMA locality info, to tell whether NUMA Balancing is working well for a particular workload, also imply the NUMA efficiency. + See + - Documentation/admin-guide/cg-numa-stat.rst menuconfig CGROUPS bool "Control Group support" -- 2.14.4.44.g2045bb6
next prev parent reply index Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-11-13 3:43 [PATCH 0/3] sched/numa: introduce advanced numa statistic 王贇 2019-11-13 3:44 ` [PATCH 1/3] sched/numa: advanced per-cgroup " 王贇 2019-11-13 3:45 ` [PATCH 2/3] sched/numa: expose per-task pages-migration-failure 王贇 2019-11-13 3:45 ` [PATCH 3/3] sched/numa: documentation for per-cgroup numa stat 王贇 2019-11-13 15:09 ` Jonathan Corbet 2019-11-14 1:52 ` 王贇 2019-11-13 18:28 ` Iurii Zaikin 2019-11-14 2:22 ` 王贇 2019-11-15 2:29 ` [PATCH v2 " 王贇 2019-11-20 9:45 ` [PATCH 0/3] sched/numa: introduce advanced numa statistic 王贇 2019-11-25 1:35 ` 王贇 2019-11-27 1:48 ` [PATCH v2 " 王贇 2019-11-27 1:49 ` [PATCH v2 1/3] sched/numa: advanced per-cgroup " 王贇 2019-11-27 10:19 ` Mel Gorman 2019-11-28 2:09 ` 王贇 2019-11-28 12:39 ` Michal Koutný 2019-11-28 13:41 ` 王贇 2019-11-28 15:58 ` Michal Koutný 2019-11-29 1:52 ` 王贇 2019-11-29 5:19 ` 王贇 2019-11-29 10:06 ` Michal Koutný 2019-12-02 2:11 ` 王贇 2019-11-27 1:50 ` [PATCH v2 2/3] sched/numa: expose per-task pages-migration-failure 王贇 2019-11-27 10:00 ` Mel Gorman 2019-12-02 2:22 ` 王贇 2019-11-27 1:50 ` [PATCH v2 3/3] sched/numa: documentation for per-cgroup numa stat 王贇 2019-11-27 4:58 ` Randy Dunlap 2019-11-27 5:54 ` 王贇 2019-12-03 5:59 ` [PATCH v3 0/2] sched/numa: introduce numa locality 王贇 2019-12-03 6:00 ` [PATCH v3 1/2] sched/numa: introduce per-cgroup NUMA locality info 王贇 2019-12-04 2:33 ` Randy Dunlap 2019-12-04 2:38 ` 王贇 2019-12-03 6:02 ` [PATCH v3 2/2] sched/numa: documentation for per-cgroup numa statistics 王贇 2019-12-03 13:43 ` Jonathan Corbet 2019-12-04 2:27 ` 王贇 2019-12-04 7:58 ` [PATCH v4 0/2] sched/numa: introduce numa locality 王贇 2019-12-04 7:59 ` [PATCH v4 1/2] sched/numa: introduce per-cgroup NUMA locality info 王贇 2019-12-05 3:28 ` Randy Dunlap 2019-12-05 3:29 ` Randy Dunlap 2019-12-05 3:52 ` 王贇 2019-12-04 8:00 ` [PATCH v4 2/2] sched/numa: documentation for per-cgroup numa statistics 王贇 2019-12-05 3:40 ` Randy Dunlap 2019-12-05 6:53 ` [PATCH v5 0/2] sched/numa: introduce numa locality 王贇 2019-12-05 6:53 ` [PATCH v5 1/2] sched/numa: introduce per-cgroup NUMA locality info 王贇 2019-12-05 6:54 ` 王贇 [this message] 2019-12-10 2:19 ` [PATCH v5 0/2] sched/numa: introduce numa locality 王贇 2019-12-13 1:43 ` [PATCH v6 " 王贇 2019-12-13 1:47 ` [PATCH v6 1/2] sched/numa: introduce per-cgroup NUMA locality info 王贇 2020-01-03 15:14 ` Michal Koutný 2020-01-04 4:51 ` 王贇 2019-12-13 1:48 ` [PATCH v6 2/2] sched/numa: documentation for per-cgroup numa 王贇 2019-12-27 2:22 ` [PATCH v6 0/2] sched/numa: introduce numa locality 王贇 2020-01-17 2:19 ` 王贇 2020-01-19 6:08 ` [PATCH v7 " 王贇 2020-01-19 6:09 ` [PATCH v7 1/2] sched/numa: introduce per-cgroup NUMA locality info 王贇 2020-01-19 6:09 ` [PATCH v7 2/2] sched/numa: documentation for per-cgroup numa, statistics 王贇 2020-01-21 0:12 ` Randy Dunlap 2020-01-21 1:58 ` 王贇 2020-01-21 1:56 ` [PATCH v8 0/2] sched/numa: introduce numa locality 王贇 2020-01-21 1:57 ` [PATCH v8 1/2] sched/numa: introduce per-cgroup NUMA locality info 王贇 2020-01-21 1:57 ` [PATCH v8 2/2] sched/numa: documentation for per-cgroup numa, statistics 王贇 2020-01-21 2:08 ` Randy Dunlap 2020-02-07 1:10 ` [PATCH v8 0/2] sched/numa: introduce numa locality 王贇 2020-02-07 1:25 ` Steven Rostedt 2020-02-07 2:31 ` 王贇 2020-02-07 2:37 ` [PATCH RESEND " 王贇
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