diff options
| author | Chris Wilson <chris@chris-wilson.co.uk> | 2017-11-24 13:00:30 +0000 |
|---|---|---|
| committer | Chris Wilson <chris@chris-wilson.co.uk> | 2017-11-24 16:09:51 +0000 |
| commit | a54b1873c0e3ffec3041cf72cb10d986d6bc4fe5 (patch) | |
| tree | 2d9f9d176c3d3b6eb2da1253678d66f545ad1f85 /drivers | |
| parent | 8c5da3bbcfd9cf763623f2d9515ace8eb3f01307 (diff) | |
drm/i915: Use exponential backoff for wait_for()
Instead of sleeping for a fixed 1ms (roughly, depending on timer slack),
start with a small sleep and exponentially increase the sleep on each
cycle.
A good example of a beneficiary is the guc mmio communication channel.
Typically we expect (and so spin) for 10us for a quick response, but this
doesn't cover everything and so sometimes we fallback to the millisecond+
sleep. This incurs a significant delay in time-critical operations like
preemption (igt/gem_exec_latency), which can be improved significantly by
using a small sleep after the spin fails.
We've made this suggestion many times, but had little experimental data
to support adding the complexity.
v2: Bump the minimum usleep to 10us on advice of
Documentation/timers/timers-howto.txt (Tvrko)
v3: Specify min, max range for usleep intervals -- some code may
crucially depend upon and so want to specify the sleep pattern.
References: 1758b90e38f5 ("drm/i915: Use a hybrid scheme for fast register waits")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: John Harrison <John.C.Harrison@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171124130031.20761-2-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/gpu/drm/i915/intel_drv.h | 11 | ||||
| -rw-r--r-- | drivers/gpu/drm/i915/intel_pm.c | 2 |
2 files changed, 8 insertions, 5 deletions
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h index 635a96fcd788..c00441a3d649 100644 --- a/drivers/gpu/drm/i915/intel_drv.h +++ b/drivers/gpu/drm/i915/intel_drv.h @@ -48,8 +48,9 @@ * having timed out, since the timeout could be due to preemption or similar and * we've never had a chance to check the condition before the timeout. */ -#define _wait_for(COND, US, W) ({ \ +#define _wait_for(COND, US, Wmin, Wmax) ({ \ unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1; \ + long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \ int ret__; \ might_sleep(); \ for (;;) { \ @@ -62,12 +63,14 @@ ret__ = -ETIMEDOUT; \ break; \ } \ - usleep_range((W), (W) * 2); \ + usleep_range(wait__, wait__ * 2); \ + if (wait__ < (Wmax)) \ + wait__ <<= 1; \ } \ ret__; \ }) -#define wait_for(COND, MS) _wait_for((COND), (MS) * 1000, 1000) +#define wait_for(COND, MS) _wait_for((COND), (MS) * 1000, 10, 1000) /* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */ #if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT) @@ -116,7 +119,7 @@ int ret__; \ BUILD_BUG_ON(!__builtin_constant_p(US)); \ if ((US) > 10) \ - ret__ = _wait_for((COND), (US), 10); \ + ret__ = _wait_for((COND), (US), 10, 10); \ else \ ret__ = _wait_for_atomic((COND), (US), 0); \ ret__; \ diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c index 03d67d8ab647..a80c322c5b43 100644 --- a/drivers/gpu/drm/i915/intel_pm.c +++ b/drivers/gpu/drm/i915/intel_pm.c @@ -9294,7 +9294,7 @@ int skl_pcode_request(struct drm_i915_private *dev_priv, u32 mbox, u32 request, ret = 0; goto out; } - ret = _wait_for(COND, timeout_base_ms * 1000, 10); + ret = _wait_for(COND, timeout_base_ms * 1000, 10, 10); if (!ret) goto out; |