Messages in this thread | | | Date | Tue, 22 Jul 2014 11:19:40 +0300 | From | Oded Gabbay <> | Subject | Re: [PATCH v2 00/25] AMDKFD kernel driver |
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On 22/07/14 10:28, Daniel Vetter wrote: > On Mon, Jul 21, 2014 at 03:03:07PM -0400, Jerome Glisse wrote: >> On Mon, Jul 21, 2014 at 09:41:29PM +0300, Oded Gabbay wrote: >>> On 21/07/14 21:22, Daniel Vetter wrote: >>>> On Mon, Jul 21, 2014 at 7:28 PM, Oded Gabbay <oded.gabbay@amd.com> wrote: >>>>>> I'm not sure whether we can do the same trick with the hw scheduler. But >>>>>> then unpinning hw contexts will drain the pipeline anyway, so I guess we >>>>>> can just stop feeding the hw scheduler until it runs dry. And then unpin >>>>>> and evict. >>>>> So, I'm afraid but we can't do this for AMD Kaveri because: >>>> >>>> Well as long as you can drain the hw scheduler queue (and you can do >>>> that, worst case you have to unmap all the doorbells and other stuff >>>> to intercept further submission from userspace) you can evict stuff. >>> >>> I can't drain the hw scheduler queue, as I can't do mid-wave preemption. >>> Moreover, if I use the dequeue request register to preempt a queue >>> during a dispatch it may be that some waves (wave groups actually) of >>> the dispatch have not yet been created, and when I reactivate the mqd, >>> they should be created but are not. However, this works fine if you use >>> the HIQ. the CP ucode correctly saves and restores the state of an >>> outstanding dispatch. I don't think we have access to the state from >>> software at all, so it's not a bug, it is "as designed". >>> >> >> I think here Daniel is suggesting to unmapp the doorbell page, and track >> each write made by userspace to it and while unmapped wait for the gpu to >> drain or use some kind of fence on a special queue. Once GPU is drain we >> can move pinned buffer, then remap the doorbell and update it to the last >> value written by userspace which will resume execution to the next job. > > Exactly, just prevent userspace from submitting more. And if you have > misbehaving userspace that submits too much, reset the gpu and tell it > that you're sorry but won't schedule any more work.
I'm not sure how you intend to know if a userspace misbehaves or not. Can you elaborate ?
Oded > > We have this already in i915 (since like all other gpus we're not > preempting right now) and it works. There's some code floating around to > even restrict the reset to _just_ the offending submission context, with > nothing else getting corrupted. > > You can do all this with the doorbells and unmapping them, but it's a > pain. Much easier if you have a real ioctl, and I haven't seen anyone with > perf data indicating that an ioctl would be too much overhead on linux. > Neither in this thread nor internally here at intel. > -Daniel >
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