On Sat, May 01, 2021 at 10:27:03AM -0500, Jason Ekstrand wrote:
On April 30, 2021 23:01:44 "Dixit, Ashutosh" <ashutosh.dixit@xxxxxxxxx>
wrote:
On Fri, 30 Apr 2021 19:19:59 -0700, Umesh Nerlige Ramappa wrote:
On Fri, Apr 30, 2021 at 07:35:41PM -0500, Jason Ekstrand wrote:
On April 30, 2021 18:00:58 "Dixit, Ashutosh"
<ashutosh.dixit@xxxxxxxxx>
wrote:
On Fri, 30 Apr 2021 15:26:09 -0700, Umesh Nerlige Ramappa wrote:
Looks like the engine can be dropped since all timestamps are in
sync.
I
just have one more question here. The timestamp itself is 36 bits.
Should
the uapi also report the timestamp width to the user OR should I
just
return the lower 32 bits of the timestamp?
Yeah, I think reporting the timestamp width is a good idea since
we're
reporting the period/frequency here.
Actually, I forgot that we are handling the overflow before returning
the
cs_cycles to the user and overflow handling was the only reason I
thought
user should know the width. Would you stil recommend returning the
width in
the uapi?
The width is needed for userspace to figure out if overflow has occured
between two successive query calls. I don't think I see this happening
in
the code.
Right... We (UMDs) currently just hard-code it to 36 bits because that's
what we've had on all platforms since close enough to forever. We bake in
the frequency based on PCI ID. Returning the number of bits, like I said,
goes nicely with the frequency. It's not necessary, assuming sufficiently
smart userspace (neither is frequency), but it seems to go with it. I
guess I don't care much either way.
Coming back to the multi-tile issue we discussed internally, I think that
is something we should care about. Since this works by reading the
timestamp register on an engine, I think leaving the engine specifier in
there is fine. Userspace should know that there's actually only one clock
and just query one of them (probably RCS). For crazy multi-device cases,
we'll either query per logical device (read tile) or we'll have to make
them look like a single device and sync the timestamps somehow in the UMD
by carrying around an offset factor.
As is, this patch is
Reviewed-by: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Thanks, I will add the width here and post the final version.
Regards,
Umesh
I still need to review the ANV patch before we can land this though.
--Jason
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