| Message ID | 1380152133-1024-2-git-send-email-benjamin.widawsky@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Sep 25, 2013 at 04:35:33PM -0700, Ben Widawsky wrote: > The policy's max frequency is not equal to the CPU's max frequency. The > ring frequency is derived from the CPU frequency, and not the policy > frequency. > > One example of how this may differ through sysfs. If the sysfs max > frequency is modified, that will be used for the max ring frequency > calculation. > (/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq). As far as I > know, no current governor uses anything but max as the default, but in > theory, they could. Similarly distributions might set policy as part of > their init process. Actually this seems to differ based on policy as well. The pstate may disable turbo mode, in which case policy->max <= policy->cpuinfo.max. But excluding user intervention, it seems that max is what we want, and it is possibly arguable that we do not want to push the core to turbo for a GPU bound workload - though I'm not sure if the ring frequency continues to scale with turbo cpu frequencies. > It's ideal to use the real frequency because when we're currently scaled > up on the GPU. In this case we likely want to race to idle, and using a > less than max ring frequency is non-optimal for this situation. Also note that scaling the cpu frequency cuts into our thermal headroom, so for ULT devices it may not be clearly beneficial. > AFAIK, this patch should have no impact on a majority of people. And also obsolete since HSW. > This behavior hasn't been changed since it was first introduced: > commit 23b2f8bb92feb83127679c53633def32d3108e70 > Author: Jesse Barnes <jbarnes@virtuousgeek.org> > Date: Tue Jun 28 13:04:16 2011 -0700 > > drm/i915: load a ring frequency scaling table v3 > > CC: Jesse Barnes <jbarnes@virtuousgeek.org> > Signed-off-by: Ben Widawsky <ben@bwidawsk.net> FWIW, Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> I think using the real range of the CPU frequency rather than the adjusted policy maximum is sensible. Just the hw implementation is just a bit silly and it is not clear exactly what the best policy should be. -Chris
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c index 31cf188..3212d3b 100644 --- a/drivers/gpu/drm/i915/intel_pm.c +++ b/drivers/gpu/drm/i915/intel_pm.c @@ -3639,16 +3639,21 @@ void gen6_update_ring_freq(struct drm_device *dev) unsigned int gpu_freq; unsigned int max_ia_freq, min_ring_freq; int scaling_factor = 180; + struct cpufreq_policy *policy; WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock)); - max_ia_freq = cpufreq_quick_get_max(0); - /* - * Default to measured freq if none found, PCU will ensure we don't go - * over - */ - if (!max_ia_freq) + policy = cpufreq_cpu_get(0); + if (policy) { + max_ia_freq = policy->cpuinfo.max_freq; + cpufreq_cpu_put(policy); + } else { + /* + * Default to measured freq if none found, PCU will ensure we + * don't go over + */ max_ia_freq = tsc_khz; + } /* Convert from kHz to MHz */ max_ia_freq /= 1000;
The policy's max frequency is not equal to the CPU's max frequency. The ring frequency is derived from the CPU frequency, and not the policy frequency. One example of how this may differ through sysfs. If the sysfs max frequency is modified, that will be used for the max ring frequency calculation. (/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq). As far as I know, no current governor uses anything but max as the default, but in theory, they could. Similarly distributions might set policy as part of their init process. It's ideal to use the real frequency because when we're currently scaled up on the GPU. In this case we likely want to race to idle, and using a less than max ring frequency is non-optimal for this situation. AFAIK, this patch should have no impact on a majority of people. This behavior hasn't been changed since it was first introduced: commit 23b2f8bb92feb83127679c53633def32d3108e70 Author: Jesse Barnes <jbarnes@virtuousgeek.org> Date: Tue Jun 28 13:04:16 2011 -0700 drm/i915: load a ring frequency scaling table v3 CC: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Ben Widawsky <ben@bwidawsk.net> --- drivers/gpu/drm/i915/intel_pm.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-)