netdev - Re: [RFC] Add BPF_PROG_TYPE_CGROUP

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Date:   Tue, 11 May 2021 11:48:10 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Daniel Vetter <daniel@...ll.ch>, Kenny Ho <y2kenny@...il.com>,
        Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andriin@...com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kenny Ho <Kenny.Ho@....com>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        Brian Welty <brian.welty@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Martin KaFai Lau <kafai@...com>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Network Development <netdev@...r.kernel.org>,
        KP Singh <kpsingh@...omium.org>, Yonghong Song <yhs@...com>,
        bpf <bpf@...r.kernel.org>, Dave Airlie <airlied@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [RFC] Add BPF_PROG_TYPE_CGROUP_IOCTL

On Fri, May 7, 2021 at 7:45 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Fri, May 07, 2021 at 06:30:56PM -0400, Alex Deucher wrote:
> > Maybe we are speaking past each other.  I'm not following.  We got
> > here because a device specific cgroup didn't make sense.  With my
> > Linux user hat on, that makes sense.  I don't want to write code to a
> > bunch of device specific interfaces if I can avoid it.  But as for
> > temporal vs spatial partitioning of the GPU, the argument seems to be
> > a sort of hand-wavy one that both spatial and temporal partitioning
> > make sense on CPUs, but only temporal partitioning makes sense on
> > GPUs.  I'm trying to understand that assertion.  There are some GPUs
>
> Spatial partitioning as implemented in cpuset isn't a desirable model. It's
> there partly because it has historically been there. It doesn't really
> require dynamic hierarchical distribution of anything and is more of a way
> to batch-update per-task configuration, which is how it's actually
> implemented. It's broken too in that it interferes with per-task affinity
> settings. So, not exactly a good example to follow. In addition, this sort
> of partitioning requires more hardware knowledge and GPUs are worse than
> CPUs in that hardwares differ more.
>
> Features like this are trivial to implement from userland side by making
> per-process settings inheritable and restricting who can update the
> settings.
>
> > that can more easily be temporally partitioned and some that can be
> > more easily spatially partitioned.  It doesn't seem any different than
> > CPUs.
>
> Right, it doesn't really matter how the resource is distributed. What
> matters is how granular and generic the distribution can be. If gpus can
> implement work-conserving proportional distribution, that's something which
> is widely useful and inherently requires dynamic scheduling from kernel
> side. If it's about setting per-vendor affinities, this is way too much
> cgroup interface for a feature which can be easily implemented outside
> cgroup. Just do per-process (or whatever handles gpus use) and confine their
> configurations from cgroup side however way.
>
> While the specific theme changes a bit, we're basically having the same
> discussion with the same conclusion over the past however many months.
> Hopefully, the point is clear by now.

Thanks, that helps a lot.

Alex