netdev - Re: [RFC PATCH 0/2] block: use eBPF to redirect IO completion

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Date:   Tue, 15 Oct 2019 09:20:00 +0800
From:   Bob Liu <bob.liu@...cle.com>
To:     Hou Tao <houtao1@...wei.com>, linux-block@...r.kernel.org,
        bpf@...r.kernel.org, netdev@...r.kernel.org, axboe@...nel.dk,
        ast@...nel.org
Cc:     hare@...e.com, osandov@...com, ming.lei@...hat.com,
        damien.lemoal@....com, bvanassche@....org, daniel@...earbox.net,
        kafai@...com, songliubraving@...com, yhs@...com
Subject: Re: [RFC PATCH 0/2] block: use eBPF to redirect IO completion

On 10/14/19 8:28 PM, Hou Tao wrote:
> For network stack, RPS, namely Receive Packet Steering, is used to
> distribute network protocol processing from hardware-interrupted CPU
> to specific CPUs and alleviating soft-irq load of the interrupted CPU.
> 
> For block layer, soft-irq (for single queue device) or hard-irq
> (for multiple queue device) is used to handle IO completion, so
> RPS will be useful when the soft-irq load or the hard-irq load
> of a specific CPU is too high, or a specific CPU set is required
> to handle IO completion.
> 
> Instead of setting the CPU set used for handling IO completion
> through sysfs or procfs, we can attach an eBPF program to the
> request-queue, provide some useful info (e.g., the CPU
> which submits the request) to the program, and let the program
> decides the proper CPU for IO completion handling.
> 

But it looks like there isn't any benefit than through sysfs/procfs?

> In order to demonostrate the effect of IO completion redirection,
> a test programm is built to redirect the IO completion handling
> to all online CPUs or a specific CPU set:
> 
> 	./test_blkdev_ccpu -d /dev/vda
> or
> 	./test_blkdev_ccpu -d /dev/nvme0n1 -s 4,8,10-13
> 
> However I am still trying to find out a killer scenario for

Speaking about scenario, perhaps attaching a filter could be useful? 
So that the data can be processed the first place.

-
Bob

> the eBPF redirection, so suggestions and comments are welcome.
> 
> Regards,
> Tao
> 
> Hou Tao (2):
>   block: add support for redirecting IO completion through eBPF
>   selftests/bpf: add test program for redirecting IO completion CPU
> 
>  block/Makefile                                |   2 +-
>  block/blk-bpf.c                               | 127 +++++++++
>  block/blk-mq.c                                |  22 +-
>  block/blk-softirq.c                           |  27 +-
>  include/linux/blkdev.h                        |   3 +
>  include/linux/bpf_blkdev.h                    |   9 +
>  include/linux/bpf_types.h                     |   1 +
>  include/uapi/linux/bpf.h                      |   2 +
>  kernel/bpf/syscall.c                          |   9 +
>  tools/include/uapi/linux/bpf.h                |   2 +
>  tools/lib/bpf/libbpf.c                        |   1 +
>  tools/lib/bpf/libbpf_probes.c                 |   1 +
>  tools/testing/selftests/bpf/Makefile          |   1 +
>  .../selftests/bpf/progs/blkdev_ccpu_rr.c      |  66 +++++
>  .../testing/selftests/bpf/test_blkdev_ccpu.c  | 246 ++++++++++++++++++
>  15 files changed, 507 insertions(+), 12 deletions(-)
>  create mode 100644 block/blk-bpf.c
>  create mode 100644 include/linux/bpf_blkdev.h
>  create mode 100644 tools/testing/selftests/bpf/progs/blkdev_ccpu_rr.c
>  create mode 100644 tools/testing/selftests/bpf/test_blkdev_ccpu.c
>