On Thu, Oct 23, 2014 at 8:47 AM, Chris Wilson <ch...@chris-wilson.co.uk> wrote:
> On Wed, Oct 22, 2014 at 04:28:51PM +0100, Robert Bragg wrote:
>> + /* XXX: Not sure that this is really acceptable...
>> + *
>> + * i915_gem_context.c currently owns pinning/unpinning legacy
>> + * context buffers and although that code has a
>> + * get_context_alignment() func to handle a different
>> + * constraint for gen6 we are assuming it's fixed for gen7
>> + * here. Another option besides pinning here would be to
>> + * instead hook into context switching and update the
>> + * OACONTROL configuration on the fly.
>> + */
>> + if (dev_priv->oa_pmu.specific_ctx) {
>> + struct intel_context *ctx = dev_priv->oa_pmu.specific_ctx;
>> + int ret;
>> +
>> + ret = i915_gem_obj_ggtt_pin(ctx->legacy_hw_ctx.rcs_state,
>> + 4096, 0);
>
> Right if you pin it here with a different alignment, when we try to pin
> it with the required hw ctx alignment it will fail. Easiest way is to
> record the ctx->legacy_hw_ctx.alignment and reuse that here.
Ok I can look into that a bit more. I'm not currently sure I can assume the
ctx will have been pinned before, to be able to record the alignment.
Skimming i915_gem_context.c, it looks like we only pin the default context
on creation and a user could open a perf even before we first switch to that
context.
I wonder if it would be ok to expose an i915_get_context_alignment() api to
deal with this?
>
>> + if (ret) {
>> + DRM_DEBUG_DRIVER("Couldn't pin %d\n", ret);
>> + ret = -EBUSY;
>
> As an exercise, think of all the possible error values from pin() and
> tell me why overriding that here is a bad, bad idea.
Hmm, I'm not quite sure why I decided to squash the error code there, it
looks pretty arbitrary. My take on your comment a.t.m is essentially that
some of the pin() errors don't really represent a busy state where it would
make sense for userspace to try again later; such as -ENODEV. Sorry if you
saw a very specific case that offended you :-) I have removed the override
locally.
Thanks for taking a look.
- Robert
> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre
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