On 02/06/2015 19:47, Dave Gordon wrote:
On 02/06/15 19:36, Siluvery, Arun wrote:
On 01/06/2015 11:22, Daniel, Thomas wrote:
Indeed, allocating an extra scratch page in the context would simplify
vma/mm management. A trick might be to allocate the scratch page at the
start, then offset the lrc regs etc - that would then be consistent
amongst gen and be easy enough to extend if we need more per-context
scratch space in future.
-Chris
Yes, I think we already have another use for more per-context space at
the start. The GuC is planning to do this. Arun, you probably should
work with Alex Dai and Dave Gordon to avoid conflicts here.
Thomas.
Thanks for the heads-up Thomas.
I have discussed with Dave and agreed to share this page;
GuC probably doesn't need whole page so first half is reserved for it's
use and second half is used for WA.
I have modified my patches to use context page for applying these WA and
don't see any issues.
During the discussions Dave proposed another approach. Even though these
WA are called per context they are only initialized once and not changed
afterwards, same set of WA are applied for each context so instead of
adding them in each context, does it make sense to create a separate
page and share across all contexts? but of course GuC will anyway add a
new page to context so I might as well share that page.
Chris/Dave, do you see any problems with sharing page with GuC or you
prefer to allocate a separate page for these WA and share across all
contexts? Please give your comments.
regards
Arun
I think we have to consider which is more future-proof i.e. which is
least likely:
(1) the area shared with the GuC grows (definitely still in flux), or
(2) workarounds need to be context-specific (possible, but unlikely)
So I'd prefer a single area set up just once to contain the pre- and
post-context restore workaround batches. If necessary, the one area
could contain multiple batches at different offsets, so we could point
different contexts at different (shared) batches as required. I think
they're unlikely to actually need per-context customisation[*], but
there might be a need for different workarounds according to workload
type or privilege level or some other criterion ... ?
.Dave.
[*] unless they need per-context memory addresses coded into them?
Considering these WA are initialized only once and not changed
afterwards and GuC area probably grows in future which may run into the
space used by WA, independent single area setup makes senses.
I also checked spec and it is not clear whether any customization is
going to be required for different contexts.
I have modified patches to setup a single page with WA when
default_context is initialized and this is used by all contexts.
I will send patches but please let me know if there are any other comments.
regards
Arun
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