Messages in this thread | | | Subject | Re: [PATCH] dmabuf: Add the capability to expose DMA-BUF stats in sysfs | From | Christian König <> | Date | Thu, 10 Dec 2020 12:02:55 +0100 |
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Am 10.12.20 um 11:56 schrieb Greg KH: > On Thu, Dec 10, 2020 at 11:27:27AM +0100, Daniel Vetter wrote: >> On Thu, Dec 10, 2020 at 11:10:45AM +0100, Greg KH wrote: >>> On Thu, Dec 10, 2020 at 10:58:50AM +0100, Christian König wrote: >>>> In general a good idea, but I have a few concern/comments here. >>>> >>>> Am 10.12.20 um 05:43 schrieb Hridya Valsaraju: >>>>> 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/<inode_number>/exporter_name >>>>> /sys/kernel/dmabuf/<inode_number>/size >>>>> /sys/kernel/dmabuf/<inode_number>/dev_map_info >>>>> >>>>> 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. >>>> Mhm, this makes it part of the UAPI. What is the justification for this? >>>> >>>> In other words do we really need those debug information in a production >>>> environment? >>> Production environments seem to want to know who is using up memory :) >> This only shows shared memory, so it does smell a lot like $specific_issue >> and we're designing a narrow solution for that and then have to carry it >> forever. > I think the "issue" is that this was a feature from ion that people > "missed" in the dmabuf move. Taking away the ability to see what kind > of allocations were being made didn't make a lot of debugging tools > happy :(
Yeah, that is certainly a very valid concern.
> But Hridya knows more, she's been dealing with the transition for a long > time now. > >> E.g. why is the list of attachments not a sysfs link? That's how we >> usually expose struct device * pointers in sysfs to userspace, not as a >> list of things. > These aren't struct devices, so I don't understand the objection here. > Where else could these go in sysfs?
Sure they are! Just take a look at an attachment:
struct dma_buf_attachment { struct dma_buf *dmabuf; struct device *dev;
This is the struct device which is importing the buffer and the patch in discussion is just printing the name of this device into sysfs.
>> Furthermore we don't have the exporter device covered anywhere, how is >> that tracked? Yes Android just uses ion for all shared buffers, but that's >> not how all of linux userspace works. > Do we have the exporter device link in the dmabuf interface? If so, > great, let's use that, but for some reason I didn't think it was there.
Correct, since we don't really need a device as an exporter (it can just be a system heap as well) we only have a const char* as name for the exporter.
>> Then I guess there's the mmaps, you can fish them out of procfs. A tool >> which collects all that information might be useful, just as demonstration >> of how this is all supposed to be used. > There's a script somewhere that does this today, again, Hridya knows > more. > >> There's also some things to make sure we're at least having thought about >> how other things fit in here. E.d. dma_resv attached to the dma-buf >> matters in general a lot. It doesn't matter on Android because >> everything's pinned all the time anyway. >> >> Also I thought sysfs was one value one file, dumping an entire list into >> dev_info_map with properties we'll need to extend (once you care about >> dma_resv you also want to know which attachments are dynamic) does not >> smell like sysfs design at all. > sysfs is one value per file, what is being exported that is larger than > that here? Did I miss something on review?
See this chunk here:
+ + list_for_each_entry(attachment, &dmabuf->attachments, node) { + if (attachment->map_counter) { + ret += sysfs_emit_at(buf, ret, "%s ", + dev_name(attachment->dev)); + } + }
And yes now that Daniel mentioned that it looks like a sysfs rules violation to me as well.
Regards, Christian.
> > thanks, > > greg k-h
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