On 21/07/14 22:28, Jerome Glisse wrote: > On Mon, Jul 21, 2014 at 10:23:43PM +0300, Oded Gabbay wrote: >> On 21/07/14 21:59, Jerome Glisse wrote: >>> On Mon, Jul 21, 2014 at 09:36:44PM +0300, Oded Gabbay wrote: >>>> On 21/07/14 21:14, Jerome Glisse wrote: >>>>> On Mon, Jul 21, 2014 at 08:42:58PM +0300, Oded Gabbay wrote: >>>>>> On 21/07/14 18:54, Jerome Glisse wrote: >>>>>>> On Mon, Jul 21, 2014 at 05:12:06PM +0300, Oded Gabbay wrote: >>>>>>>> On 21/07/14 16:39, Christian König wrote: >>>>>>>>> Am 21.07.2014 14:36, schrieb Oded Gabbay: >>>>>>>>>> On 20/07/14 20:46, Jerome Glisse wrote: >>>>>>>>>>> On Thu, Jul 17, 2014 at 04:57:25PM +0300, Oded Gabbay wrote: >>>>>>>>>>>> Forgot to cc mailing list on cover letter. Sorry. >>>>>>>>>>>> >>>>>>>>>>>> As a continuation to the existing discussion, here is a v2 patch series >>>>>>>>>>>> restructured with a cleaner history and no totally-different-early-versions >>>>>>>>>>>> of the code. >>>>>>>>>>>> >>>>>>>>>>>> Instead of 83 patches, there are now a total of 25 patches, where 5 of them >>>>>>>>>>>> are modifications to radeon driver and 18 of them include only amdkfd code. >>>>>>>>>>>> There is no code going away or even modified between patches, only added. >>>>>>>>>>>> >>>>>>>>>>>> The driver was renamed from radeon_kfd to amdkfd and moved to reside under >>>>>>>>>>>> drm/radeon/amdkfd. This move was done to emphasize the fact that this driver >>>>>>>>>>>> is an AMD-only driver at this point. Having said that, we do foresee a >>>>>>>>>>>> generic hsa framework being implemented in the future and in that case, we >>>>>>>>>>>> will adjust amdkfd to work within that framework. >>>>>>>>>>>> >>>>>>>>>>>> As the amdkfd driver should support multiple AMD gfx drivers, we want to >>>>>>>>>>>> keep it as a seperate driver from radeon. Therefore, the amdkfd code is >>>>>>>>>>>> contained in its own folder. The amdkfd folder was put under the radeon >>>>>>>>>>>> folder because the only AMD gfx driver in the Linux kernel at this point >>>>>>>>>>>> is the radeon driver. Having said that, we will probably need to move it >>>>>>>>>>>> (maybe to be directly under drm) after we integrate with additional AMD gfx >>>>>>>>>>>> drivers. >>>>>>>>>>>> >>>>>>>>>>>> For people who like to review using git, the v2 patch set is located at: >>>>>>>>>>>> http://cgit.freedesktop.org/~gabbayo/linux/log/?h=kfd-next-3.17-v2 >>>>>>>>>>>> >>>>>>>>>>>> Written by Oded Gabbayh <oded.gabbay@xxxxxxx> >>>>>>>>>>> >>>>>>>>>>> So quick comments before i finish going over all patches. There is many >>>>>>>>>>> things that need more documentation espacialy as of right now there is >>>>>>>>>>> no userspace i can go look at. >>>>>>>>>> So quick comments on some of your questions but first of all, thanks for the >>>>>>>>>> time you dedicated to review the code. >>>>>>>>>>> >>>>>>>>>>> There few show stopper, biggest one is gpu memory pinning this is a big >>>>>>>>>>> no, that would need serious arguments for any hope of convincing me on >>>>>>>>>>> that side. >>>>>>>>>> We only do gpu memory pinning for kernel objects. There are no userspace >>>>>>>>>> objects that are pinned on the gpu memory in our driver. If that is the case, >>>>>>>>>> is it still a show stopper ? >>>>>>>>>> >>>>>>>>>> The kernel objects are: >>>>>>>>>> - pipelines (4 per device) >>>>>>>>>> - mqd per hiq (only 1 per device) >>>>>>>>>> - mqd per userspace queue. On KV, we support up to 1K queues per process, for >>>>>>>>>> a total of 512K queues. Each mqd is 151 bytes, but the allocation is done in >>>>>>>>>> 256 alignment. So total *possible* memory is 128MB >>>>>>>>>> - kernel queue (only 1 per device) >>>>>>>>>> - fence address for kernel queue >>>>>>>>>> - runlists for the CP (1 or 2 per device) >>>>>>>>> >>>>>>>>> The main questions here are if it's avoid able to pin down the memory and if the >>>>>>>>> memory is pinned down at driver load, by request from userspace or by anything >>>>>>>>> else. >>>>>>>>> >>>>>>>>> As far as I can see only the "mqd per userspace queue" might be a bit >>>>>>>>> questionable, everything else sounds reasonable. >>>>>>>>> >>>>>>>>> Christian. >>>>>>>> >>>>>>>> Most of the pin downs are done on device initialization. >>>>>>>> The "mqd per userspace" is done per userspace queue creation. However, as I >>>>>>>> said, it has an upper limit of 128MB on KV, and considering the 2G local >>>>>>>> memory, I think it is OK. >>>>>>>> The runlists are also done on userspace queue creation/deletion, but we only >>>>>>>> have 1 or 2 runlists per device, so it is not that bad. >>>>>>> >>>>>>> 2G local memory ? You can not assume anything on userside configuration some >>>>>>> one might build an hsa computer with 512M and still expect a functioning >>>>>>> desktop. >>>>>> First of all, I'm only considering Kaveri computer, not "hsa" computer. >>>>>> Second, I would imagine we can build some protection around it, like >>>>>> checking total local memory and limit number of queues based on some >>>>>> percentage of that total local memory. So, if someone will have only >>>>>> 512M, he will be able to open less queues. >>>>>> >>>>>> >>>>>>> >>>>>>> I need to go look into what all this mqd is for, what it does and what it is >>>>>>> about. But pinning is really bad and this is an issue with userspace command >>>>>>> scheduling an issue that obviously AMD fails to take into account in design >>>>>>> phase. >>>>>> Maybe, but that is the H/W design non-the-less. We can't very well >>>>>> change the H/W. >>>>> >>>>> You can not change the hardware but it is not an excuse to allow bad design to >>>>> sneak in software to work around that. So i would rather penalize bad hardware >>>>> design and have command submission in the kernel, until AMD fix its hardware to >>>>> allow proper scheduling by the kernel and proper control by the kernel. >>>> I'm sorry but I do *not* think this is a bad design. S/W scheduling in >>>> the kernel can not, IMO, scale well to 100K queues and 10K processes. >>> >>> I am not advocating for having kernel decide down to the very last details. I am >>> advocating for kernel being able to preempt at any time and be able to decrease >>> or increase user queue priority so overall kernel is in charge of resources >>> management and it can handle rogue client in proper fashion. >>> >>>> >>>>> Because really where we want to go is having GPU closer to a CPU in term of scheduling >>>>> capacity and once we get there we want the kernel to always be able to take over >>>>> and do whatever it wants behind process back. >>>> Who do you refer to when you say "we" ? AFAIK, the hw scheduling >>>> direction is where AMD is now and where it is heading in the future. >>>> That doesn't preclude the option to allow the kernel to take over and do >>>> what he wants. I agree that in KV we have a problem where we can't do a >>>> mid-wave preemption, so theoretically, a long running compute kernel can >>>> make things messy, but in Carrizo, we will have this ability. Having >>>> said that, it will only be through the CP H/W scheduling. So AMD is >>>> _not_ going to abandon H/W scheduling. You can dislike it, but this is >>>> the situation. >>> >>> We was for the overall Linux community but maybe i should not pretend to talk >>> for anyone interested in having a common standard. >>> >>> My point is that current hardware do not have approriate hardware support for >>> preemption hence, current hardware should use ioctl to schedule job and AMD >>> should think a bit more on commiting to a design and handwaving any hardware >>> short coming as something that can be work around in the software. The pinning >>> thing is broken by design, only way to work around it is through kernel cmd >>> queue scheduling that's a fact. >> >>> >>> Once hardware support proper preemption and allows to move around/evict buffer >>> use on behalf of userspace command queue then we can allow userspace scheduling >>> but until then my personnal opinion is that it should not be allowed and that >>> people will have to pay the ioctl price which i proved to be small, because >>> really if you 100K queue each with one job, i would not expect that all those >>> 100K job will complete in less time than it takes to execute an ioctl ie by >>> even if you do not have the ioctl delay what ever you schedule will have to >>> wait on previously submited jobs. >> >> But Jerome, the core problem still remains in effect, even with your >> suggestion. If an application, either via userspace queue or via ioctl, >> submits a long-running kernel, than the CPU in general can't stop the >> GPU from running it. And if that kernel does while(1); than that's it, >> game's over, and no matter how you submitted the work. So I don't really >> see the big advantage in your proposal. Only in CZ we can stop this wave >> (by CP H/W scheduling only). What are you saying is basically I won't >> allow people to use compute on Linux KV system because it _may_ get the >> system stuck. >> >> So even if I really wanted to, and I may agree with you theoretically on >> that, I can't fulfill your desire to make the "kernel being able to >> preempt at any time and be able to decrease or increase user queue >> priority so overall kernel is in charge of resources management and it >> can handle rogue client in proper fashion". Not in KV, and I guess not >> in CZ as well. >> >> Oded > > I do understand that but using kernel ioctl provide the same kind of control > as we have now ie we can bind/unbind buffer on per command buffer submission > basis, just like with current graphic or compute stuff. > > Yes current graphic and compute stuff can launch a while and never return back > and yes currently we have nothing against that but we should and solution would > be simple just kill the gpu thread. > OK, so in that case, the kernel can simple unmap all the queues by simply writing an UNMAP_QUEUES packet to the HIQ. Even if the queues are userspace, they will not be mapped to the internal CP scheduler. Does that satisfy the kernel control level you want ? Oded >> >>> >>>>> >>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> It might be better to add a drivers/gpu/drm/amd directory and add common >>>>>>>>>>> stuff there. >>>>>>>>>>> >>>>>>>>>>> Given that this is not intended to be final HSA api AFAICT then i would >>>>>>>>>>> say this far better to avoid the whole kfd module and add ioctl to radeon. >>>>>>>>>>> This would avoid crazy communication btw radeon and kfd. >>>>>>>>>>> >>>>>>>>>>> The whole aperture business needs some serious explanation. Especialy as >>>>>>>>>>> you want to use userspace address there is nothing to prevent userspace >>>>>>>>>>> program from allocating things at address you reserve for lds, scratch, >>>>>>>>>>> ... only sane way would be to move those lds, scratch inside the virtual >>>>>>>>>>> address reserved for kernel (see kernel memory map). >>>>>>>>>>> >>>>>>>>>>> The whole business of locking performance counter for exclusive per process >>>>>>>>>>> access is a big NO. Which leads me to the questionable usefullness of user >>>>>>>>>>> space command ring. >>>>>>>>>> That's like saying: "Which leads me to the questionable usefulness of HSA". I >>>>>>>>>> find it analogous to a situation where a network maintainer nacking a driver >>>>>>>>>> for a network card, which is slower than a different network card. Doesn't >>>>>>>>>> seem reasonable this situation is would happen. He would still put both the >>>>>>>>>> drivers in the kernel because people want to use the H/W and its features. So, >>>>>>>>>> I don't think this is a valid reason to NACK the driver. >>>>>>> >>>>>>> Let me rephrase, drop the the performance counter ioctl and modulo memory pinning >>>>>>> i see no objection. In other word, i am not NACKING whole patchset i am NACKING >>>>>>> the performance ioctl. >>>>>>> >>>>>>> Again this is another argument for round trip to the kernel. As inside kernel you >>>>>>> could properly do exclusive gpu counter access accross single user cmd buffer >>>>>>> execution. >>>>>>> >>>>>>>>>> >>>>>>>>>>> I only see issues with that. First and foremost i would >>>>>>>>>>> need to see solid figures that kernel ioctl or syscall has a higher an >>>>>>>>>>> overhead that is measurable in any meaning full way against a simple >>>>>>>>>>> function call. I know the userspace command ring is a big marketing features >>>>>>>>>>> that please ignorant userspace programmer. But really this only brings issues >>>>>>>>>>> and for absolutely not upside afaict. >>>>>>>>>> Really ? You think that doing a context switch to kernel space, with all its >>>>>>>>>> overhead, is _not_ more expansive than just calling a function in userspace >>>>>>>>>> which only puts a buffer on a ring and writes a doorbell ? >>>>>>> >>>>>>> I am saying the overhead is not that big and it probably will not matter in most >>>>>>> usecase. For instance i did wrote the most useless kernel module that add two >>>>>>> number through an ioctl (http://people.freedesktop.org/~glisse/adder.tar) and >>>>>>> it takes ~0.35microseconds with ioctl while function is ~0.025microseconds so >>>>>>> ioctl is 13 times slower. >>>>>>> >>>>>>> Now if there is enough data that shows that a significant percentage of jobs >>>>>>> submited to the GPU will take less that 0.35microsecond then yes userspace >>>>>>> scheduling does make sense. But so far all we have is handwaving with no data >>>>>>> to support any facts. >>>>>>> >>>>>>> >>>>>>> Now if we want to schedule from userspace than you will need to do something >>>>>>> about the pinning, something that gives control to kernel so that kernel can >>>>>>> unpin when it wants and move object when it wants no matter what userspace is >>>>>>> doing. >>>>>>> >>>>>>>>>>> >>> >>> -- >>> To unsubscribe, send a message with 'unsubscribe linux-mm' in >>> the body to majordomo@xxxxxxxxx. 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