linux-kernel - Re: [PATCH v2 0/4] cgroup/cpuset: Improve CPU isolation in isolated partitions

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Message-ID: <21ebd168-8b3f-0efc-20f1-89173e79eaed@redhat.com>
Date:   Thu, 9 Nov 2023 20:24:54 -0500
From:   Waiman Long <longman@...hat.com>
To:     "Zhang, Rui" <rui.zhang@...el.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "lizefan.x@...edance.com" <lizefan.x@...edance.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "tj@...nel.org" <tj@...nel.org>, "corbet@....net" <corbet@....net>,
        "jiangshanlai@...il.com" <jiangshanlai@...il.com>
Cc:     "pehunt@...hat.com" <pehunt@...hat.com>,
        "frederic@...nel.org" <frederic@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] cgroup/cpuset: Improve CPU isolation in isolated
 partitions

On 11/9/23 04:02, Zhang, Rui wrote:
> Hi, Waiman,
>
> May I know which kernel this patch series is based on?
>
> I'd like to test this feature, but cannot apply it cleanly on top of
> v6.6.

It was originally based on the cgroup/for-6.7 branch. It should be 
applicable to v6.7 kernel now.

Cheers,
Longman

> thanks,
> rui
>
> On Wed, 2023-10-25 at 14:25 -0400, Waiman Long wrote:
>> v2:
>>   - Add 2 read-only workqueue sysfs files to expose the user requested
>>     cpumask as well as the isolated CPUs to be excluded from
>>     wq_unbound_cpumask.
>>   - Ensure that caller of the new workqueue_unbound_exclude_cpumask()
>>     hold cpus_read_lock.
>>   - Update the cpuset code to make sure the cpus_read_lock is held
>>     whenever workqueue_unbound_exclude_cpumask() may be called.
>>
>> Isolated cpuset partition can currently be created to contain an
>> exclusive set of CPUs not used in other cgroups and with load
>> balancing
>> disabled to reduce interference from the scheduler.
>>
>> The main purpose of this isolated partition type is to dynamically
>> emulate what can be done via the "isolcpus" boot command line option,
>> specifically the default domain flag. One effect of the "isolcpus"
>> option
>> is to remove the isolated CPUs from the cpumasks of unbound
>> workqueues
>> since running work functions in an isolated CPU can be a major source
>> of interference. Changing the unbound workqueue cpumasks can be done
>> at
>> run time by writing an appropriate cpumask without the isolated CPUs
>> to
>> /sys/devices/virtual/workqueue/cpumask. So one can set up an isolated
>> cpuset partition and then write to the cpumask sysfs file to achieve
>> similar level of CPU isolation. However, this manual process can be
>> error prone.
>>
>> This patch series implements automatic exclusion of isolated CPUs
>> from
>> unbound workqueue cpumasks when an isolated cpuset partition is
>> created
>> and then adds those CPUs back when the isolated partition is
>> destroyed.
>>
>> There are also other places in the kernel that look at the
>> HK_FLAG_DOMAIN
>> cpumask or other HK_FLAG_* cpumasks and exclude the isolated CPUs
>> from
>> certain actions to further reduce interference. CPUs in an isolated
>> cpuset partition will not be able to avoid those interferences yet.
>> That
>> may change in the future as the need arises.
>>
>> Waiman Long (4):
>>    workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs
>>      from wq_unbound_cpumask
>>    selftests/cgroup: Minor code cleanup and reorganization of
>>      test_cpuset_prs.sh
>>    cgroup/cpuset: Keep track of CPUs in isolated partitions
>>    cgroup/cpuset: Take isolated CPUs out of workqueue unbound cpumask
>>
>>   Documentation/admin-guide/cgroup-v2.rst       |  10 +-
>>   include/linux/workqueue.h                     |   2 +-
>>   kernel/cgroup/cpuset.c                        | 286 +++++++++++++---
>> --
>>   kernel/workqueue.c                            |  91 +++++-
>>   .../selftests/cgroup/test_cpuset_prs.sh       | 216 ++++++++-----
>>   5 files changed, 438 insertions(+), 167 deletions(-)
>>