My current theory is that this masks interrupt delivery to the local CPU during a critical phase. Purely papering over the symptoms with a delay plucked out of thin air from testing on tgl1-gem, refined slightly by just waiting for the next ack (though technically the next CS event may not be the corresponding event for this submit, but an intermediate completion).
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com> Cc: Andi Shyti <andi.sh...@intel.com> Acked-by: Mika Kuoppala <mika.kuopp...@linux.intel.com> --- drivers/gpu/drm/i915/gt/intel_lrc.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index fa385218ce92..6b995017571d 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -1186,6 +1186,28 @@ static void execlists_submit_ports(struct intel_engine_cs *engine) /* we need to manually load the submit queue */ if (execlists->ctrl_reg) writel(EL_CTRL_LOAD, execlists->ctrl_reg); + + /* + * Now this is evil magic. + * + * Adding the same udelay() to process_csb before we clear + * execlists->pending (that is after we receive the HW ack for this + * submit and before we can submit again) does not relieve the symptoms + * (machine lockup). So is the active difference here the wait under + * the irq-off spinlock? That gives more credance to the theory that + * the issue is interrupt delivery. Also note that we still rely on + * disabling RPS, again that seems like an issue with simultaneous + * GT interrupts being delivered to the same CPU. + */ + if (IS_TIGERLAKE(engine->i915)) { + u64 start = local_clock(); + + udelay(250); + + while (READ_ONCE(*execlists->pending) && /* wait for ack */ + (local_clock() - start) >> 22 == 0) /* ~4ms timeout */ + cpu_relax(); + } } static bool ctx_single_port_submission(const struct intel_context *ce) -- 2.23.0 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx