On Wed, Jun 26, 2019 at 12:25 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Wed, Jun 26, 2019 at 11:05:20AM -0400, Kenny Ho wrote: > > The bandwidth is measured by keeping track of the amount of bytes moved > > by ttm within a time period. We defined two type of bandwidth: burst > > and average. Average bandwidth is calculated by dividing the total > > amount of bytes moved within a cgroup by the lifetime of the cgroup. > > Burst bandwidth is similar except that the byte and time measurement is > > reset after a user configurable period. > > So I'm not too sure exposing this is a great idea, at least depending upon > what you're trying to do with it. There's a few concerns here: > > - I think bo movement stats might be useful, but they're not telling you > everything. Applications can also copy data themselves and put buffers > where they want them, especially with more explicit apis like vk. > > - which kind of moves are we talking about here? Eviction related bo moves > seem not counted here, and if you have lots of gpus with funny > interconnects you might also get other kinds of moves, not just system > ram <-> vram. Eviction move is counted but I think I placed the delay in the wrong place (the tracking of byte moved is in previous patch in ttm_bo_handle_move_mem, which is common to all move as far as I can tell.) > - What happens if we slow down, but someone else needs to evict our > buffers/move them (ttm is atm not great at this, but Christian König is > working on patches). I think there's lots of priority inversion > potential here. > > - If the goal is to avoid thrashing the interconnects, then this isn't the > full picture by far - apps can use copy engines and explicit placement, > again that's how vulkan at least is supposed to work. > > I guess these all boil down to: What do you want to achieve here? The > commit message doesn't explain the intended use-case of this. Thrashing prevention is the intent. I am not familiar with Vulkan so I will have to get back to you on that. I don't know how those explicit placement translate into the kernel. At this stage, I think it's still worth while to have this as a resource even if some applications bypass the kernel. I certainly welcome more feedback on this topic. Regards, Kenny _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
