Re: [Linaro-mm-sig] [PATCH v3] dmabuf: Add the capability to expose DMA-BUF stats in sysfs
From: Christian König
Date: Thu Feb 04 2021 - 03:14:40 EST
Am 03.02.21 um 21:14 schrieb Hridya Valsaraju:
On Wed, Feb 3, 2021 at 2:25 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
On Mon, Feb 01, 2021 at 01:02:30PM -0800, Hridya Valsaraju wrote:
On Mon, Feb 1, 2021 at 10:37 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
On Thu, Jan 28, 2021 at 1:03 PM Sumit Semwal <sumit.semwal@xxxxxxxxxx> wrote:
On Thu, 28 Jan 2021 at 17:23, Christian König
<ckoenig.leichtzumerken@xxxxxxxxx> wrote:
Am 28.01.21 um 12:00 schrieb Sumit Semwal:
Hi Hridya,
On Wed, 27 Jan 2021 at 17:36, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fpatchwork%2Fpatch%2F1088791%2F&data=04%7C01%7Cchristian.koenig%40amd.com%7C32ff828b838e44b1de6f08d8c8805913%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479800886768855%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=imVoJbadV221%2F6u32diSyEICLk7WUNakz8G742RPSaA%3D&reserved=0
[2]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fandroid-review.googlesource.com%2Fq%2Ftopic%3A%2522dmabuf-sysfs%2522&data=04%7C01%7Cchristian.koenig%40amd.com%7C32ff828b838e44b1de6f08d8c8805913%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479800886778838%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=X78MH6IvdcE1mGMngrVdBYooi93vpjvfLU9kQHjZyKo%3D&reserved=0+(status:open%20OR%20status:merged)
[3]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fandroid-review.googlesource.com%2Fc%2Fplatform%2Fsystem%2Fmemory%2Flibmeminfo%2F%2B%2F1549734&data=04%7C01%7Cchristian.koenig%40amd.com%7C32ff828b838e44b1de6f08d8c8805913%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479800886778838%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=JH7m5yspXKDqVX5DB380cnU4kWNSyh6ctDaphJvOyw8%3D&reserved=0
Signed-off-by: Hridya Valsaraju <hridya@xxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
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!
From the technical side it looks clean to me, feel free to add my
acked-by while pushing.
But I would at least try to convince Daniel on the design. At least some
of his concerns seems to be valid and keep in mind that we need to
support this interface forever.
Naturally.
Since he didn't comment over Hridya's last clarification about the
tracepoints to track total GPU memory allocations being orthogonal to
this series, I assumed he agreed with it.
The tracepoint being orthogonal didn't really look convincing to me,
since I do expect we'll need that at a much more generic level, at
allocators. Whether that's dma-buf heaps or in drm or wherever. And we
probably also need that to somehow align with cgroups accounting.
But I guess for this it should be easy to extend however we see fit,
so retrofitting allocator sources and anything else we want/need for
the overall gpu memory account shouldn't be a problem. Also, it's
first, so the proof for showing it all works together is more on the
tracepoints :-)
Daniel, do you still have objections around adding this patch in?
Needs docs (especially the uapi I think would be useful to document),
igt tests, that kind of stuff still I think? It's meant to be generic
uapi across drivers, generally we're a pile stricter for that (and yes
dma-buf heaps I think didn't do all that, so maybe there's an argument
for doing this a bit more sloppy or at least "the testsuite is
somewhere else").
Thank you for taking another look Daniel!
I will try adding an IGT test for the sysfs files. Other than the
documentation in
Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers(included in the
patch), is there another place you would like to see the documentation
copied to?
So just read the other thread, and sounds like Christian König brought up
a solid concern with dma-buf fds generally not staying around for much.
Thank you for the reply Daniel! Could you please elaborate on the
connection with the other thread you mentioned? I am a little confused
since this patch does not deal with tracking DMA-BUF fds.
In general DMA-buf fd are meant to be a temporary transport vehicle to
interchange the data between processes.
This here sounds like Android is using them as a long term reference.
That is not necessary a good idea and causes multiple issues.
On of those issues you try to address here, but Daniel is question now
why do you have this problem in the first place?
Regards,
Christian.
Regards,
Hridya
So I'm leaning more towards "this sounds like it's going to be useful for
Android only, nothing else" concern.
-Daniel