On 2017年05月12日 16:43, Christian König wrote:
Am 12.05.2017 um 10:37 schrieb zhoucm1:
On 2017年05月12日 16:33, Christian König wrote:
Am 12.05.2017 um 10:25 schrieb zhoucm1:
On 2017年05月10日 05:47, Kasiviswanathan, Harish wrote:
Hi,
Please review the patch set that supports amdgpu VM update via CPU. This
feature provides improved performance for compute (HSA) where mapping /
unmapping is carried out (by Kernel) independent of command submissions (done
directly by user space). This version doesn't support shadow copy of VM page
tables for CPU based update.
I think your improved performance is from less waiting for cs,
generally, SDMA engine updating page table is faster than CPU,
otherwise we don't need sdma for updating PT.
So whether your this improvement proves we have some redundant sync
when mapping / unmapping, if yes, we should fix that, then not sure
if CPU method is need or not.
The problem is that the KFD is designed synchronously for page table
updates. In other words they need to wait for the update to finish
and that takes time.
Apart from that your comment is absolutely correct, we found that
the SDMA is sometimes much faster to do the update than the CPU.
If the sdma is faster, even they wait for finish, which time is
shorter than CPU, isn't it? Of course, the precondition is sdma is
exclusive. They can reserve a sdma for PT updating.
No, if I understood Felix numbers correctly the setup and wait time
for SDMA is a bit (but not much) longer than doing it with the CPU.
What would really help is to fix the KFD design and work with async
page tables updates there as well.
OK, no problem, just curious.
Regards,
David Zhou
Regards,
Christian.
Regards,
David Zhou
Regards,
Christian.
Regards,
David Zhou
Best Regards,
Harish
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