On Sun, Oct 1, 2017 at 6:49 AM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: > On Sat, Sep 30, 2017 at 10:57:38AM +0800, Bob Liu wrote: >> On 2017/9/27 0:16, Jerome Glisse wrote: >> > On Tue, Sep 26, 2017 at 05:56:26PM +0800, Bob Liu wrote: >> >> On Tue, Sep 12, 2017 at 7:36 AM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >> >>> On Sun, Sep 10, 2017 at 07:22:58AM +0800, Bob Liu wrote: >> >>>> On Wed, Sep 6, 2017 at 3:36 AM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >> >>>>> On Thu, Jul 20, 2017 at 08:48:20PM -0700, Dan Williams wrote: >> >>>>>> On Thu, Jul 20, 2017 at 6:41 PM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >> [...] >> >>>>> So i pushed a branch with WIP for nouveau to use HMM: >> >>>>> >> >>>>> https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-nouveau >> >>>>> >> >>>> >> >>>> Nice to see that. >> >>>> Btw, do you have any plan for a CDM-HMM driver? CPU can write to >> >>>> Device memory directly without extra copy. >> >>> >> >>> Yes nouveau CDM support on PPC (which is the only CDM platform commercialy >> >>> available today) is on the TODO list. Note that the driver changes for CDM >> >>> are minimal (probably less than 100 lines of code). From the driver point >> >>> of view this is memory and it doesn't matter if it is CDM or not. >> >>> >> >> >> >> It seems have to migrate/copy memory between system-memory and >> >> device-memory even in HMM-CDM solution. >> >> Because device-memory is not added into buddy system, the page fault >> >> for normal malloc() always allocate memory from system-memory!! >> >> If the device then access the same virtual address, the data is copied >> >> to device-memory. >> >> >> >> Correct me if I misunderstand something. >> >> @Balbir, how do you plan to make zero-copy work if using HMM-CDM? >> > >> > Device can access system memory so copy to device is _not_ mandatory. Copying >> > data to device is for performance only ie the device driver take hint from >> > userspace and monitor device activity to decide which memory should be migrated >> > to device memory to maximize performance. >> > >> > Moreover in some previous version of the HMM patchset we had an helper that >> >> Could you point in which version? I'd like to have a look. > > I will need to dig in. > Thank you. >> >> > allowed to directly allocate device memory on device page fault. I intend to >> > post this helper again. With that helper you can have zero copy when device >> > is the first to access the memory. >> > >> > Plan is to get what we have today work properly with the open source driver >> > and make it perform well. Once we get some experience with real workload we >> > might look into allowing CPU page fault to be directed to device memory but >> > at this time i don't think we need this. >> > >> >> For us, we need this feature that CPU page fault can be direct to device memory. >> So that don't need to copy data from system memory to device memory. >> Do you have any suggestion on the implementation? I'll try to make a prototype patch. > > Why do you need that ? What is the device and what are the requirement ? > You may think it as a CCIX device or CAPI device. The requirement is eliminate any extra copy. A typical usecase/requirement is malloc() and madvise() allocate from device memory, then CPU write data to device memory directly and trigger device to read the data/do calculation. -- Regards, --Bob -- 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>
