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drm/i915/gt: Only swap to a random sibling once upon creation

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The danger in switching at random upon intel_context_pin is that the
context may still actually be inflight, as it will not be scheduled out
until a context switch after it is complete -- that may be a long time
after we do a final intel_context_unpin.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2118
Fixes: 6d06779e86 ("drm/i915: Load balancing across a virtual engine")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.3+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200713160549.17344-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2020-07-13 17:05:49 +01:00
parent d2921096e7
commit 90a987205c
1 changed files with 4 additions and 14 deletions
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18
drivers/gpu/drm/i915/gt/intel_lrc.c
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@ -5432,13 +5432,8 @@ static void virtual_engine_initial_hint(struct virtual_engine *ve)
* typically be the first we inspect for submission.
*/
swp = prandom_u32_max(ve->num_siblings);
if (!swp)
return;
swap(ve->siblings[swp], ve->siblings[0]);
if (!intel_engine_has_relative_mmio(ve->siblings[0]))
virtual_update_register_offsets(ve->context.lrc_reg_state,
ve->siblings[0]);
if (swp)
swap(ve->siblings[swp], ve->siblings[0]);
}
static int virtual_context_alloc(struct intel_context *ce)
@ -5451,15 +5446,9 @@ static int virtual_context_alloc(struct intel_context *ce)
static int virtual_context_pin(struct intel_context *ce)
{
struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
int err;
/* Note: we must use a real engine class for setting up reg state */
err = __execlists_context_pin(ce, ve->siblings[0]);
if (err)
return err;
virtual_engine_initial_hint(ve);
return 0;
return __execlists_context_pin(ce, ve->siblings[0]);
}
static void virtual_context_enter(struct intel_context *ce)
@ -5806,6 +5795,7 @@ intel_execlists_create_virtual(struct intel_engine_cs **siblings,
ve->base.flags |= I915_ENGINE_IS_VIRTUAL;
virtual_engine_initial_hint(ve);
return &ve->context;
err_put: