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https://issues.apache.org/jira/browse/YARN-810?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wei Yan updated YARN-810:
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Attachment: YARN-810-6.patch
Update a patch to fix the test failures.
> Support CGroup ceiling enforcement on CPU
> -----------------------------------------
>
> Key: YARN-810
> URL: https://issues.apache.org/jira/browse/YARN-810
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: nodemanager
> Affects Versions: 2.1.0-beta, 2.0.5-alpha
> Reporter: Chris Riccomini
> Assignee: Sandy Ryza
> Attachments: YARN-810-3.patch, YARN-810-4.patch, YARN-810-5.patch,
> YARN-810-6.patch, YARN-810.patch, YARN-810.patch
>
>
> Problem statement:
> YARN currently lets you define an NM's pcore count, and a pcore:vcore ratio.
> Containers are then allowed to request vcores between the minimum and maximum
> defined in the yarn-site.xml.
> In the case where a single-threaded container requests 1 vcore, with a
> pcore:vcore ratio of 1:4, the container is still allowed to use up to 100% of
> the core it's using, provided that no other container is also using it. This
> happens, even though the only guarantee that YARN/CGroups is making is that
> the container will get "at least" 1/4th of the core.
> If a second container then comes along, the second container can take
> resources from the first, provided that the first container is still getting
> at least its fair share (1/4th).
> There are certain cases where this is desirable. There are also certain cases
> where it might be desirable to have a hard limit on CPU usage, and not allow
> the process to go above the specified resource requirement, even if it's
> available.
> Here's an RFC that describes the problem in more detail:
> http://lwn.net/Articles/336127/
> Solution:
> As it happens, when CFS is used in combination with CGroups, you can enforce
> a ceiling using two files in cgroups:
> {noformat}
> cpu.cfs_quota_us
> cpu.cfs_period_us
> {noformat}
> The usage of these two files is documented in more detail here:
> https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/sec-cpu.html
> Testing:
> I have tested YARN CGroups using the 2.0.5-alpha implementation. By default,
> it behaves as described above (it is a soft cap, and allows containers to use
> more than they asked for). I then tested CFS CPU quotas manually with YARN.
> First, you can see that CFS is in use in the CGroup, based on the file names:
> {noformat}
> [criccomi@eat1-qa464 ~]$ sudo -u app ls -l /cgroup/cpu/hadoop-yarn/
> total 0
> -r--r--r-- 1 app app 0 Jun 13 16:46 cgroup.procs
> drwxr-xr-x 2 app app 0 Jun 13 17:08 container_1371141151815_0004_01_000002
> -rw-r--r-- 1 app app 0 Jun 13 16:46 cpu.cfs_period_us
> -rw-r--r-- 1 app app 0 Jun 13 16:46 cpu.cfs_quota_us
> -rw-r--r-- 1 app app 0 Jun 13 16:46 cpu.rt_period_us
> -rw-r--r-- 1 app app 0 Jun 13 16:46 cpu.rt_runtime_us
> -rw-r--r-- 1 app app 0 Jun 13 16:46 cpu.shares
> -r--r--r-- 1 app app 0 Jun 13 16:46 cpu.stat
> -rw-r--r-- 1 app app 0 Jun 13 16:46 notify_on_release
> -rw-r--r-- 1 app app 0 Jun 13 16:46 tasks
> [criccomi@eat1-qa464 ~]$ sudo -u app cat
> /cgroup/cpu/hadoop-yarn/cpu.cfs_period_us
> 100000
> [criccomi@eat1-qa464 ~]$ sudo -u app cat
> /cgroup/cpu/hadoop-yarn/cpu.cfs_quota_us
> -1
> {noformat}
> Oddly, it appears that the cfs_period_us is set to .1s, not 1s.
> We can place processes in hard limits. I have process 4370 running YARN
> container container_1371141151815_0003_01_000003 on a host. By default, it's
> running at ~300% cpu usage.
> {noformat}
> CPU
> 4370 criccomi 20 0 1157m 551m 14m S 240.3 0.8 87:10.91 ...
> {noformat}
> When I set the CFS quote:
> {noformat}
> echo 1000 >
> /cgroup/cpu/hadoop-yarn/container_1371141151815_0003_01_000003/cpu.cfs_quota_us
> CPU
> 4370 criccomi 20 0 1157m 563m 14m S 1.0 0.8 90:08.39 ...
> {noformat}
> It drops to 1% usage, and you can see the box has room to spare:
> {noformat}
> Cpu(s): 2.4%us, 1.0%sy, 0.0%ni, 92.2%id, 4.2%wa, 0.0%hi, 0.1%si,
> 0.0%st
> {noformat}
> Turning the quota back to -1:
> {noformat}
> echo -1 >
> /cgroup/cpu/hadoop-yarn/container_1371141151815_0003_01_000003/cpu.cfs_quota_us
> {noformat}
> Burns the cores again:
> {noformat}
> Cpu(s): 11.1%us, 1.7%sy, 0.0%ni, 83.9%id, 3.1%wa, 0.0%hi, 0.2%si,
> 0.0%st
> CPU
> 4370 criccomi 20 0 1157m 563m 14m S 253.9 0.8 89:32.31 ...
> {noformat}
> On my dev box, I was testing CGroups by running a python process eight times,
> to burn through all the cores, since it was doing as described above (giving
> extra CPU to the process, even with a cpu.shares limit). Toggling the
> cfs_quota_us seems to enforce a hard limit.
> Implementation:
> What do you guys think about introducing a variable to YarnConfiguration:
> bq. yarn.nodemanager.linux-container.executor.cgroups.cpu-ceiling-enforcement
> The default would be false. Setting to true, would cause YARN's LCE to set:
> {noformat}
> cpu.cfs_quota_us=(container-request-vcores/nm-vcore-to-pcore-ratio) * 1000000
> cpu.cfs_period_us=1000000
> {noformat}
> For example, if a container asks for 2 vcores, and the vcore:pcore ratio is
> 4, you'd get:
> {noformat}
> cpu.cfs_quota_us=(2/4) * 1000000 = 500000
> cpu.cfs_period_us=1000000
> {noformat}
> This would cause CFS to cap the process at 50% of clock cycles.
> What do you guys think?
> 1. Does this seem like a reasonable request? We have some use-cases for it.
> 2. It's unclear to me how cpu.shares interacts with cpu.cfs_*. I think the
> ceiling is hard, no matter what shares is set to. I assume shares only comes
> into play if the CFS quota has not been reached, and the process begins
> competing with others for CPU resources.
> 3. Should this be an LCE config (yarn.nodemanager.linux-container-executor),
> or should it be a generic scheduler config
> (yarn.scheduler.enforce-ceiling-vcores).
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