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. > > > > >>> > >>>>>>> > >>>>>>>>> > >>>>>>>>> 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. For more info on Linux MM, > > see: http://www.linux-mm.org/ . > > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>