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From: Peter Zijlstra <peterz@infradead.org>
To: "Pratik R. Sampat" <psampat@linux.ibm.com>
Cc: bristot@redhat.com, christian@brauner.io, ebiederm@xmission.com,
	lizefan.x@bytedance.com, tj@kernel.org, hannes@cmpxchg.org,
	mingo@kernel.org, juri.lelli@redhat.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	cgroups@vger.kernel.org, containers@lists.linux.dev,
	containers@lists.linux-foundation.org, pratik.r.sampat@gmail.com
Subject: Re: [RFC 0/5] kernel: Introduce CPU Namespace
Date: Sun, 10 Oct 2021 00:41:38 +0200	[thread overview]
Message-ID: <20211009224138.GZ174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20211009151243.8825-1-psampat@linux.ibm.com>

On Sat, Oct 09, 2021 at 08:42:38PM +0530, Pratik R. Sampat wrote:

> Current shortcomings in the prototype:
> --------------------------------------
> 1. Containers also frequently use cfs period and quotas to restrict CPU
>    runtime also known as millicores in modern container runtimes.
>    The RFC interface currently does not account for this in
>    the scheme of things.
> 2. While /proc/stat is now namespace aware and userspace programs like
>    top will see the CPU utilization for their view of virtual CPUs;
>    if the system or any other application outside the namespace
>    bumps up the CPU utilization it will still show up in sys/user time.
>    This should ideally be shown as stolen time instead.
>    The current implementation plugs into the display of stats rather
>    than accounting which causes incorrect reporting of stolen time.
> 3. The current implementation assumes that no hotplug operations occur
>    within a container and hence the online and present cpus within a CPU
>    namespace are always the same and query the same CPU namespace mask
> 4. As this is a proof of concept, currently we do not differentiate
>    between cgroup cpus_allowed and effective_cpus and plugs them into
>    the same virtual CPU map of the namespace
> 5. As described in a fair use implication earlier, knowledge of the
>    CPU topology can potentially be taken an misused with a flood.
>    While scrambling the CPUset in the namespace can help by
>    obfuscation of information, the topology can still be roughly figured
>    out with the use of IPI latencies to determine siblings or far away
>    cores

6. completely destroys and ignores any machine topology information.

  parent reply	other threads:[~2021-10-09 22:41 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-09 15:12 [RFC 0/5] kernel: Introduce CPU Namespace Pratik R. Sampat
2021-10-09 15:12 ` [RFC 1/5] ns: " Pratik R. Sampat
2021-10-09 22:37   ` Peter Zijlstra
2021-10-09 15:12 ` [RFC 2/5] ns: Add scrambling functionality to CPU namespace Pratik R. Sampat
2021-10-09 15:12 ` [RFC 3/5] cpuset/cpuns: Make cgroup CPUset CPU namespace aware Pratik R. Sampat
2021-10-09 15:12 ` [RFC 4/5] cpu/cpuns: Make sysfs " Pratik R. Sampat
2021-10-09 15:12 ` [RFC 5/5] proc/cpuns: Make procfs load stats " Pratik R. Sampat
2021-10-09 22:41 ` Peter Zijlstra [this message]
2021-10-11 10:11 ` [RFC 0/5] kernel: Introduce CPU Namespace Christian Brauner
2021-10-11 14:17   ` Michal Koutný
2021-10-11 17:42     ` Tejun Heo
2021-10-12  8:42   ` Pratik Sampat
2021-10-14 22:14     ` Tejun Heo
2021-10-18 15:29       ` Pratik Sampat
2021-10-18 16:29         ` Tejun Heo
2021-10-20 10:44           ` Pratik Sampat
2021-10-20 16:35             ` Tejun Heo
2021-10-21  7:44               ` Pratik Sampat
2021-10-21 17:06                 ` Tejun Heo
2021-10-21 17:15             ` Eric W. Biederman

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