On 17/08/16 15:44, Chris Wilson wrote:
On Wed, Aug 17, 2016 at 03:36:51PM +0100, Tvrtko Ursulin wrote:
On 17/08/16 11:05, Chris Wilson wrote:
On Wed, Aug 17, 2016 at 10:57:34AM +0100, Tvrtko Ursulin wrote:
On 17/08/16 10:41, Chris Wilson wrote:
On Wed, Aug 17, 2016 at 10:34:18AM +0100, Tvrtko Ursulin wrote:
Or add an initialized engine array to dev_priv, in addition to the
existing map for best of both worlds.
We have the ring_mask which already tells us that mapping, so I think
the second array is overkill.
Yes, I said "in addition to the existing map". In addition we could
have an array of only initialized engines to avoid any skipping at
runtime. Since iterators end with intel_engine_initialized anyway.
And I'm saying we already have that information in ring_mask.
The ffs smarts you've been developing? I am not sure devising very
smart macros and expanding all that code to all the call sites is
that great. It is effectively just re-implementing arrays at runtime
using CPU instructions.
What would be the big deal of just building the array when engines
are initialized for simplicity? Just the allure of getting away with
no iterator variable?
It's just the redundant information. We definitely want the (sparse)
id->engine lookup table just for convenience in execbuf and friends.
Given that, having a second array is overkill. A list may be a
reasonable compromise, and I guess pushing for using an ffs iterator
where it matters (where we know we have a sparse set).
Don't get what you consider a list vs array? I was talking about an
contiguous array of engine pointers (only initialized ones).
Can't see that it is redundant or overkill since it is not that uncommon
to have two separate data structure/indices pointing the the same thing
for ease of manipulation/use.
As I said, you build the list once at init time, or you build it
effectively at the every iterator site. When you call ffs() you make the
CPU do the skipping just on a lower level than the current C code does.
Regards,
Tvrtko
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