From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@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 20:50:52 +0200 [thread overview]
Message-ID: <YMJfDHr1+xxm6SBi@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210603212416.25934-3-longman@redhat.com>
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.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>,
Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>,
Shuah Khan <shuah-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>,
Phil Auld <pauld-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Juri Lelli <juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing
Date: Thu, 10 Jun 2021 20:50:52 +0200 [thread overview]
Message-ID: <YMJfDHr1+xxm6SBi@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210603212416.25934-3-longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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.
next prev parent reply other threads:[~2021-06-10 18:51 UTC|newest]
Thread overview: 25+ 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 [this message]
2021-06-10 18:50 ` Peter Zijlstra
2021-06-10 19:16 ` Waiman Long
2021-06-10 19:39 ` Peter Zijlstra
2021-06-10 19:00 ` Peter Zijlstra
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
2021-06-17 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
2021-06-03 21:24 ` Waiman Long
2021-06-16 20:57 ` Tejun Heo
2021-06-16 20:57 ` Tejun Heo
2021-06-17 20:45 ` Waiman Long
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
2021-06-10 14:19 ` Phil Auld
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