From 2b57e6df97598a9507853d567ab164a3d68d7e9c Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri, 8 Nov 2019 10:35:10 +0000
Subject: drm/i915/pmu: Cheat when reading the actual frequency to avoid fw
Git-commit: c1c82d267ae8b42de0802c31fabeb843189adb9d
Patch-mainline: v5.6-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322
We want to avoid taking forcewake when querying the performance stats,
as we wish to avoid perturbing the system under observation. (And with
the forcewake being kept alive for 1ms after use, sampling the frequency
from a 200Hz timer keeps forcewake 40% active.)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191108103511.20951-1-chris@chris-wilson.co.uk
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/i915/i915_pmu.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index d6d2e6fb8674..5f35d37b777d 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -333,9 +333,22 @@ frequency_sample(struct intel_gt *gt, unsigned int period_ns)
val = rps->cur_freq;
if (intel_gt_pm_get_if_awake(gt)) {
- val = intel_uncore_read_notrace(uncore, GEN6_RPSTAT1);
- val = intel_get_cagf(rps, val);
- intel_gt_pm_put_async(gt);
+ u32 stat;
+
+ /*
+ * We take a quick peek here without using forcewake
+ * so that we don't perturb the system under observation
+ * (forcewake => !rc6 => increased power use). We expect
+ * that if the read fails because it is outside of the
+ * mmio power well, then it will return 0 -- in which
+ * case we assume the system is running at the intended
+ * frequency. Fortunately, the read should rarely fail!
+ */
+ stat = intel_uncore_read_fw(uncore, GEN6_RPSTAT1);
+ if (stat)
+ val = intel_get_cagf(rps, stat);
+
+ intel_gt_pm_put(gt);
}
add_sample_mult(&pmu->sample[__I915_SAMPLE_FREQ_ACT],
--
2.28.0