On 24-05-18, 15:42, Dave Jiang wrote: > > > On 05/24/2018 03:38 PM, Eric Pilmore wrote: > > Hi! > > > > (Sorry if duplicate. Trying to remove HTML content.). > > > > Wondering if somebody out there might be able to help me. I have a > > situation where I have a pool of physical DMA engines, with each > > appearing as a separate DMA device in the system, on top of which I > > want to create a much larger number of virtual DMA channels. So, I > > want to export a large number of virtual DMA channels which are > > serviced by a smaller pool of DMA engines. > > > > Now one way that I see how this could be addressed is that for each > > instance of a DMA engine in the pool I instantiate say V number of > > virtual DMA channels to be associated with the given instance. So, if > > the size of my pool of DMA engines is P, then in the end I'll end up > > PxV virtual DMA channels available to clients. > > > > My concern is, as clients come in and do dma_request_channel() calls, > > when the (virtual) DMA channels are handed out it appears that they'll > > be handed out sequentially (ignoring for the moment the whole cpu node > > thing). Thus, all the V channels of DMA engine instance 0 will be > > handed out before the subsystem gets around to handing out channels > > for the next DMA engine, instance 1, and so on. As such, I'll end up > > with a scenario where my allocated virtual channels are not evenly > > distributed across my pool of P DMA engines. Is there a mechanism to > > more evenly distribute the allocation of DMA channels to clients > > across a pool of DMA engines? So, if only P number of (virtual) DMA > > channels were to be allocated to clients, then the assignment to > > physical DMA engines would end up being 1-1, rather than P channels > > all being serviced by one physical DMA engine. > > > > Is there something in the Linux DMA framework that might address this? > > I've been digging through what documentation I can find and the > > source code, and not seeing anything. Do I need to "hide" the physical > > DMA engines into appearing as one, and then within my driver manage > > the round-robin allocation of them to virtual channels myself? > > I don't know the answer to your problem but it's something I'm > definitely interested in the answer to. I wonder if the vdma stuff need > to be plumbed to be NUMA aware and all that fun stuff and provide the > same ability for requests as the current dma_request_channel() calls for > physical DMAs. Would having a filter which would allocate the channel based on some policy help here. So in this case Eric wants the channels to be evenly distributed on controllers available. -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
