Re: [PATCH v3] dmabuf: Add the capability to expose DMA-BUF stats in sysfs

[Sumit Semwal <sumit.semwal@linaro.org>]

Hi Hridya,

On Wed, 27 Jan 2021 at 17:36, Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Jan 26, 2021 at 12:42:36PM -0800, Hridya Valsaraju wrote:
> > This patch allows statistics to be enabled for each DMA-BUF in
> > sysfs by enabling the config CONFIG_DMABUF_SYSFS_STATS.
> >
> > The following stats will be exposed by the interface:
> >
> > /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
> > /sys/kernel/dmabuf/buffers/<inode_number>/size
> > /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
> > /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter
> >
> > The inode_number is unique for each DMA-BUF and was added earlier [1]
> > in order to allow userspace to track DMA-BUF usage across different
> > processes.
> >
> > Currently, this information is exposed in
> > /sys/kernel/debug/dma_buf/bufinfo.
> > However, since debugfs is considered unsafe to be mounted in production,
> > it is being duplicated in sysfs.
> >
> > This information will be used to derive DMA-BUF
> > per-exporter stats and per-device usage stats for Android Bug reports.
> > The corresponding userspace changes can be found at [2].
> > Telemetry tools will also capture this information(along with other
> > memory metrics) periodically as well as on important events like a
> > foreground app kill (which might have been triggered by Low Memory
> > Killer). It will also contribute to provide a snapshot of the system
> > memory usage on other events such as OOM kills and Application Not
> > Responding events.
> >
> > A shell script that can be run on a classic Linux environment to read
> > out the DMA-BUF statistics can be found at [3](suggested by John
> > Stultz).
> >
> > The patch contains the following improvements over the previous version:
> > 1) Each attachment is represented by its own directory to allow creating
> > a symlink to the importing device and to also provide room for future
> > expansion.
> > 2) The number of distinct mappings of each attachment is exposed in a
> > separate file.
> > 3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
> > inorder to make the interface expandable in future.
> >
> > All of the improvements above are based on suggestions/feedback from
> > Daniel Vetter and Christian König.
> >
> > [1]: https://lore.kernel.org/patchwork/patch/1088791/
> > [2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
> > [3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734
> >
> > Signed-off-by: Hridya Valsaraju <hridya@google.com>
> > Reported-by: kernel test robot <lkp@intel.com>

Thanks for the patch!

Christian: If you're satisfied with the explanation around not
directly embedding kobjects into the dma_buf and dma_buf_attachment
structs, then with Greg's r-b from sysfs PoV, I think we can merge it.
Please let me know if you feel otherwise!

> > ---
> > Changes in v3:
> > Fix a warning reported by the kernel test robot.
> >
> > Changes in v2:
> > -Move statistics to /sys/kernel/dmabuf/buffers in oder to allow addition
> > of other DMA-BUF-related sysfs stats in future. Based on feedback from
> > Daniel Vetter.
> > -Each attachment has its own directory to represent attaching devices as
> > symlinks and to introduce map_count as a separate file. Based on
> > feedback from Daniel Vetter and Christian König. Thank you both!
> > -Commit messages updated to point to userspace code in AOSP that will
> > read the DMA-BUF sysfs stats.
> >
> >
> >  .../ABI/testing/sysfs-kernel-dmabuf-buffers   |  52 ++++
> >  drivers/dma-buf/Kconfig                       |  11 +
> >  drivers/dma-buf/Makefile                      |   1 +
> >  drivers/dma-buf/dma-buf-sysfs-stats.c         | 285 ++++++++++++++++++
> >  drivers/dma-buf/dma-buf-sysfs-stats.h         |  62 ++++
> >  drivers/dma-buf/dma-buf.c                     |  37 +++
> >  include/linux/dma-buf.h                       |  20 ++
> >  7 files changed, 468 insertions(+)
> >  create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> >  create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.c
> >  create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.h
>
> I don't know the dma-buf code at all, but from a sysfs/kobject point of
> view, this patch looks good to me:
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Best,
Sumit.
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