On Fri, Oct 24, 2014 at 03:33:14AM +0100, Robert Bragg wrote:
> 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?
I would either add intel_context_pin_state()/unpin_state() or expose
ctx->...state_alignment. Leaning towards the former so that we don't have
too many places mucking around inside ctx.
> >
> >> + 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.
Or EINTR/EAGAIN and try again immediately. ;)
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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