netdev - Re: [RFC] Add BPF_PROG_TYPE_CGROUP

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Date:   Fri, 7 May 2021 18:13:47 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Kenny Ho <y2kenny@...il.com>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Dave Airlie <airlied@...il.com>, Kenny Ho <Kenny.Ho@....com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        Alex Deucher <alexander.deucher@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Brian Welty <brian.welty@...el.com>
Subject: Re: [RFC] Add BPF_PROG_TYPE_CGROUP_IOCTL

On Fri, May 07, 2021 at 11:33:46AM -0400, Kenny Ho wrote:
> On Fri, May 7, 2021 at 4:59 AM Daniel Vetter <daniel@...ll.ch> wrote:
> >
> > Hm I missed that. I feel like time-sliced-of-a-whole gpu is the easier gpu
> > cgroups controler to get started, since it's much closer to other cgroups
> > that control bandwidth of some kind. Whether it's i/o bandwidth or compute
> > bandwidht is kinda a wash.
> sriov/time-sliced-of-a-whole gpu does not really need a cgroup
> interface since each slice appears as a stand alone device.  This is
> already in production (not using cgroup) with users.  The cgroup
> proposal has always been parallel to that in many sense: 1) spatial
> partitioning as an independent but equally valid use case as time
> sharing, 2) sub-device resource control as opposed to full device
> control motivated by the workload characterization paper.  It was
> never about time vs space in terms of use cases but having new API for
> users to be able to do spatial subdevice partitioning.
> 
> > CU mask feels a lot more like an isolation/guaranteed forward progress
> > kind of thing, and I suspect that's always going to be a lot more gpu hw
> > specific than anything we can reasonably put into a general cgroups
> > controller.
> The first half is correct but I disagree with the conclusion.  The
> analogy I would use is multi-core CPU.  The capability of individual
> CPU cores, core count and core arrangement may be hw specific but
> there are general interfaces to support selection of these cores.  CU
> mask may be hw specific but spatial partitioning as an idea is not.
> Most gpu vendors have the concept of sub-device compute units (EU, SE,
> etc.); OpenCL has the concept of subdevice in the language.  I don't
> see any obstacle for vendors to implement spatial partitioning just
> like many CPU vendors support the idea of multi-core.
> 
> > Also for the time slice cgroups thing, can you pls give me pointers to
> > these old patches that had it, and how it's done? I very obviously missed
> > that part.
> I think you misunderstood what I wrote earlier.  The original proposal
> was about spatial partitioning of subdevice resources not time sharing
> using cgroup (since time sharing is already supported elsewhere.)

Well SRIOV time-sharing is for virtualization. cgroups is for
containerization, which is just virtualization but with less overhead and
more security bugs.

More or less.

So either I get things still wrong, or we'll get time-sharing for
virtualization, and partitioning of CU for containerization. That doesn't
make that much sense to me.

Since time-sharing is the first thing that's done for virtualization I
think it's probably also the most reasonable to start with for containers.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch