On 08/01/2016 21:59, Chris Wilson wrote:
On Fri, Jan 08, 2016 at 06:47:22PM +0000, John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
There is a construct in the linux kernel called 'struct fence' that is
intended to keep track of work that is executed on hardware. I.e. it
solves the basic problem that the drivers 'struct
drm_i915_gem_request' is trying to address. The request structure does
quite a lot more than simply track the execution progress so is very
definitely still required. However, the basic completion status side
could be updated to use the ready made fence implementation and gain
all the advantages that provides.
This patch makes the first step of integrating a struct fence into the
request. It replaces the explicit reference count with that of the
fence. It also replaces the 'is completed' test with the fence's
equivalent. Currently, that simply chains on to the original request
implementation. A future patch will improve this.
But this forces everyone to do the heavyweight polling until the request
is completed?
Not sure what you mean by heavy weight polling. And as described, this
is only an intermediate step.
The seqno is already CPU cacheable and with the exception
of interrupt polling, the question of whether a fence is complete can be
determined by just inspecting that value. Only one place (the
interrupt/signalling path) should ever be concerned about the
complication of how we emit the breadcrumb and interrupt from the ring.
There is still only one piece of code that needs to worry about the
internal details. This is change is simply moving that around to make it
easier to be interrupt driven later on (which is required for the
scheduler).
-Chris
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