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>, "Jonathan Corbet" <corbet@lwn.net>, "Iurii Zaikin" <yzaikin@google.com> Subject: [PATCH v2 3/3] sched/numa: documentation for per-cgroup numa stat Date: Fri, 15 Nov 2019 10:29:11 +0800 Message-ID: <263bb462-6f7c-c313-a0cc-04beb308076b@linux.alibaba.com> (raw) In-Reply-To: <896a7da3-f139-32e7-8a64-b3562df1a091@linux.alibaba.com> 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> --- Since v1: * thanks to Iurii for the better sentences * thanks to Jonathan for the better format 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..1aed3b1d23c4 --- /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 5e27d74e2b74..475b8351be6d 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3191,6 +3191,10 @@ 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 614179dc79a9..719593e8be20 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: ============================ -- 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 ` 王贇 [this message] 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 ` [PATCH v5 2/2] sched/numa: documentation for per-cgroup numa, statistics 王贇 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
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=263bb462-6f7c-c313-a0cc-04beb308076b@linux.alibaba.com \ --to=yun.wang@linux.alibaba.com \ --cc=bsegall@google.com \ --cc=corbet@lwn.net \ --cc=dietmar.eggemann@arm.com \ --cc=juri.lelli@redhat.com \ --cc=keescook@chromium.org \ --cc=linux-doc@vger.kernel.org \ --cc=linux-fsdevel@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=mcgrof@kernel.org \ --cc=mgorman@suse.de \ --cc=mingo@redhat.com \ --cc=mkoutny@suse.com \ --cc=paulmck@linux.ibm.com \ --cc=peterz@infradead.org \ --cc=rostedt@goodmis.org \ --cc=vincent.guittot@linaro.org \ --cc=yzaikin@google.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-Fsdevel Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \ linux-fsdevel@vger.kernel.org public-inbox-index linux-fsdevel Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel AGPL code for this site: git clone https://public-inbox.org/public-inbox.git