From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <llong@redhat.com>
Cc: Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Roman Gushchin <guro@fb.com>, Phil Auld <pauld@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>
Subject: Re: [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing
Date: Thu, 10 Jun 2021 21:39:35 +0200 [thread overview]
Message-ID: <YMJqd1JJcFTThH8j@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <820aff72-fce2-ac2f-88e6-787249e04308@redhat.com>
On Thu, Jun 10, 2021 at 03:16:29PM -0400, Waiman Long wrote:
> On 6/10/21 2:50 PM, Peter Zijlstra wrote:
> > On Thu, Jun 03, 2021 at 05:24:13PM -0400, Waiman Long wrote:
> > > Cpuset v1 uses the sched_load_balance control file to determine if load
> > > balancing should be enabled. Cpuset v2 gets rid of sched_load_balance
> > > as its use may require disabling load balancing at cgroup root.
> > >
> > > For workloads that require very low latency like DPDK, the latency
> > > jitters caused by periodic load balancing may exceed the desired
> > > latency limit.
> > >
> > > When cpuset v2 is in use, the only way to avoid this latency cost is to
> > > use the "isolcpus=" kernel boot option to isolate a set of CPUs. After
> > > the kernel boot, however, there is no way to add or remove CPUs from
> > > this isolated set. For workloads that are more dynamic in nature, that
> > > means users have to provision enough CPUs for the worst case situation
> > > resulting in excess idle CPUs.
> > >
> > > To address this issue for cpuset v2, a new cpuset.cpus.partition type
> > > "root-nolb" is added which allows the creation of a cpuset partition with
> > > no load balancing. This will allow system administrators to dynamically
> > > adjust the size of the no load balancing partition to the current need
> > > of the workload without rebooting the system.
> > I'm confused, why do you need this? Just create a parition for each cpu.
> >
> From a management point of view, it is more cumbersome to do one cpu per
> partition. I have suggested this idea of 1 cpu per partition to the
> container developers, but they don't seem to like it.
Oh, because it then creates a cgroup tree per CPU and you get to move
tasks between cgroups?
OK I suppose.
next prev parent reply other threads:[~2021-06-10 19:40 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-03 21:24 [PATCH 0/5] cgroup/cpuset: Enable cpuset partition with no load balancing Waiman Long
2021-06-03 21:24 ` [PATCH 1/5] cgroup/cpuset: Don't call validate_change() for some flag changes Waiman Long
2021-06-16 20:39 ` Tejun Heo
2021-06-17 2:53 ` Waiman Long
2021-06-03 21:24 ` [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing Waiman Long
2021-06-10 18:50 ` Peter Zijlstra
2021-06-10 19:16 ` Waiman Long
2021-06-10 19:39 ` Peter Zijlstra [this message]
2021-06-10 19:00 ` Peter Zijlstra
2021-06-10 19:21 ` Waiman Long
2021-06-16 20:47 ` Tejun Heo
2021-06-17 2:57 ` Waiman Long
2021-06-03 21:24 ` [PATCH 3/5] cgroup/cpuset: Allow non-top parent partition root to distribute out all CPUs Waiman Long
2021-06-16 20:57 ` Tejun Heo
2021-06-17 20:45 ` Waiman Long
2021-06-03 21:24 ` [PATCH 4/5] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Waiman Long
2021-06-03 21:24 ` [PATCH 5/5] kselftest/cgroup: Add cpuset v2 partition root state test Waiman Long
2021-06-10 14:19 ` [PATCH 0/5] cgroup/cpuset: Enable cpuset partition with no load balancing Phil Auld
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