[Intel-gfx] [PATCH] drm/i915/guc: Disable PL1 power limit when loading GuC firmware
Dixit, Ashutosh
ashutosh.dixit at intel.com
Thu Apr 6 04:50:25 UTC 2023
On Mon, 27 Mar 2023 10:47:25 -0700, Rodrigo Vivi wrote:
>
Hi Rodrigo,
Sorry for the delay, I got pulled away into a couple of other things and
could only now get back to this.
>
> +Daniel
>
> On Mon, Mar 27, 2023 at 09:58:52AM -0700, Dixit, Ashutosh wrote:
> > On Sun, 26 Mar 2023 04:52:59 -0700, Rodrigo Vivi wrote:
> > >
> >
> > Hi Rodrigo,
> >
> > > On Fri, Mar 24, 2023 at 04:31:22PM -0700, Dixit, Ashutosh wrote:
> > > > On Fri, 24 Mar 2023 11:15:02 -0700, Belgaumkar, Vinay wrote:
> > > > >
> > > >
> > > > Hi Vinay,
> > > >
> > > > Thanks for the review. Comments inline below.
> > > >
> > > > > On 3/15/2023 8:59 PM, Ashutosh Dixit wrote:
> > > > > > On dGfx, the PL1 power limit being enabled and set to a low value results
> > > > > > in a low GPU operating freq. It also negates the freq raise operation which
> > > > > > is done before GuC firmware load. As a result GuC firmware load can time
> > > > > > out. Such timeouts were seen in the GL #8062 bug below (where the PL1 power
> > > > > > limit was enabled and set to a low value). Therefore disable the PL1 power
> > > > > > limit when allowed by HW when loading GuC firmware.
> > > > > v3 label missing in subject.
> > > > > >
> > > > > > v2:
> > > > > > - Take mutex (to disallow writes to power1_max) across GuC reset/fw load
> > > > > > - Add hwm_power_max_restore to error return code path
> > > > > >
> > > > > > v3 (Jani N):
> > > > > > - Add/remove explanatory comments
> > > > > > - Function renames
> > > > > > - Type corrections
> > > > > > - Locking annotation
> > > > > >
> > > > > > Link: https://gitlab.freedesktop.org/drm/intel/-/issues/8062
> > > > > > Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
> > > > > > ---
> > > > > > drivers/gpu/drm/i915/gt/uc/intel_uc.c | 9 +++++++
> > > > > > drivers/gpu/drm/i915/i915_hwmon.c | 39 +++++++++++++++++++++++++++
> > > > > > drivers/gpu/drm/i915/i915_hwmon.h | 7 +++++
> > > > > > 3 files changed, 55 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> > > > > > index 4ccb4be4c9cba..aa8e35a5636a0 100644
> > > > > > --- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> > > > > > +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> > > > > > @@ -18,6 +18,7 @@
> > > > > > #include "intel_uc.h"
> > > > > > #include "i915_drv.h"
> > > > > > +#include "i915_hwmon.h"
> > > > > > static const struct intel_uc_ops uc_ops_off;
> > > > > > static const struct intel_uc_ops uc_ops_on;
> > > > > > @@ -461,6 +462,7 @@ static int __uc_init_hw(struct intel_uc *uc)
> > > > > > struct intel_guc *guc = &uc->guc;
> > > > > > struct intel_huc *huc = &uc->huc;
> > > > > > int ret, attempts;
> > > > > > + bool pl1en;
> > > > >
> > > > > Init to 'false' here
> > > >
> > > > See next comment.
> > > >
> > > > >
> > > > >
> > > > > > GEM_BUG_ON(!intel_uc_supports_guc(uc));
> > > > > > GEM_BUG_ON(!intel_uc_wants_guc(uc));
> > > > > > @@ -491,6 +493,9 @@ static int __uc_init_hw(struct intel_uc *uc)
> > > > > > else
> > > > > > attempts = 1;
> > > > > > + /* Disable a potentially low PL1 power limit to allow freq to be
> > > > > > raised */
> > > > > > + i915_hwmon_power_max_disable(gt->i915, &pl1en);
> > > > > > +
> > > > > > intel_rps_raise_unslice(&uc_to_gt(uc)->rps);
> > > > > > while (attempts--) {
> > > > > > @@ -547,6 +552,8 @@ static int __uc_init_hw(struct intel_uc *uc)
> > > > > > intel_rps_lower_unslice(&uc_to_gt(uc)->rps);
> > > > > > }
> > > > > > + i915_hwmon_power_max_restore(gt->i915, pl1en);
> > > > > > +
> > > > > > guc_info(guc, "submission %s\n", str_enabled_disabled(intel_uc_uses_guc_submission(uc)));
> > > > > > guc_info(guc, "SLPC %s\n", str_enabled_disabled(intel_uc_uses_guc_slpc(uc)));
> > > > > > @@ -563,6 +570,8 @@ static int __uc_init_hw(struct intel_uc *uc)
> > > > > > /* Return GT back to RPn */
> > > > > > intel_rps_lower_unslice(&uc_to_gt(uc)->rps);
> > > > > > + i915_hwmon_power_max_restore(gt->i915, pl1en);
> > > > >
> > > > > if (pl1en)
> > > > >
> > > > > i915_hwmon_power_max_enable().
> > > >
> > > > IMO it's better not to have checks in the main __uc_init_hw() function (if
> > > > we do this we'll need to add 2 checks in __uc_init_hw()). If you really
> > > > want we could do something like this inside
> > > > i915_hwmon_power_max_disable/i915_hwmon_power_max_restore. But for now I
> > > > am not making any changes.
> > > >
> > > > (I can send a patch with the changes if you want to take a look but IMO it
> > > > will add more logic/code but without real benefits (it will save a rmw if
> > > > the limit was already disabled, but IMO this code is called so infrequently
> > > > (only during GuC resets) as to not have any significant impact)).
> > > >
> > > > >
> > > > > > +
> > > > > > __uc_sanitize(uc);
> > > > > > if (!ret) {
> > > > > > diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c
> > > > > > index ee63a8fd88fc1..769b5bda4d53f 100644
> > > > > > --- a/drivers/gpu/drm/i915/i915_hwmon.c
> > > > > > +++ b/drivers/gpu/drm/i915/i915_hwmon.c
> > > > > > @@ -444,6 +444,45 @@ hwm_power_write(struct hwm_drvdata *ddat, u32 attr, int chan, long val)
> > > > > > }
> > > > > > }
> > > > > > +void i915_hwmon_power_max_disable(struct drm_i915_private *i915, bool
> > > > > > *old)
> > > > > Shouldn't we call this i915_hwmon_package_pl1_disable()?
> > > >
> > > > I did think of using "pl1" in the function name but then decided to retain
> > > > "power_max" because other hwmon functions for PL1 limit also use
> > > > "power_max" (hwm_power_max_read/hwm_power_max_write) and currently
> > > > "hwmon_power_max" is mapped to the PL1 limit. So "power_max" is used to
> > > > show that all these functions deal with the PL1 power limit.
> > > >
> > > > There is a comment in __uc_init_hw() explaining "power_max" means the PL1
> > > > power limit.
> > > >
> > > > > > + __acquires(i915->hwmon->hwmon_lock)
> > > > > > +{
> > > > > > + struct i915_hwmon *hwmon = i915->hwmon;
> > > > > > + intel_wakeref_t wakeref;
> > > > > > + u32 r;
> > > > > > +
> > > > > > + if (!hwmon || !i915_mmio_reg_valid(hwmon->rg.pkg_rapl_limit))
> > > > > > + return;
> > > > > > +
> > > > > > + /* Take mutex to prevent concurrent hwm_power_max_write */
> > > > > > + mutex_lock(&hwmon->hwmon_lock);
> > > > > > +
> > > > > > + with_intel_runtime_pm(hwmon->ddat.uncore->rpm, wakeref)
> > > > > > + r = intel_uncore_rmw(hwmon->ddat.uncore,
> > > > > > + hwmon->rg.pkg_rapl_limit,
> > > > > > + PKG_PWR_LIM_1_EN, 0);
> > > > > Most of this code (lock and rmw parts) is already inside static void
> > > > > hwm_locked_with_pm_intel_uncore_rmw() , can we reuse that here?
> > > >
> > > > This was the case in v1 of the patch:
> > > >
> > > > https://patchwork.freedesktop.org/patch/526393/?series=115003&rev=1
> > > >
> > > > But now this cannot be done because if you notice we acquire the mutex in
> > > > i915_hwmon_power_max_disable() and release the mutex in
> > > > i915_hwmon_power_max_restore().
> > > >
> > > > I explained the reason why this the mutex is handled this way in my reply
> > > > to Jani Nikula here:
> > > >
> > > > https://patchwork.freedesktop.org/patch/526598/?series=115003&rev=2
> > > >
> > > > Quoting below:
> > > >
> > > > ```
> > > > > > + /* hwmon_lock mutex is unlocked in hwm_power_max_restore */
> > > > >
> > > > > Not too happy about that... any better ideas?
> > > >
> > > > Afais, taking the mutex is the only fully correct solution (when we disable
> > > > the power limit, userspace can go re-enable it). Examples of partly
> > > > incorrect solutions (which don't take the mutex) include:
> > > >
> > > > a. Don't take the mutex, don't do anything, ignore any changes to the value
> > > > if it has changed during GuC reset/fw load (just overwrite the changed
> > > > value). Con: changed value is lost.
> > > >
> > > > b. Detect if the value has changed (the limit has been re-enabled) after we
> > > > have disabled the limit and in that case skip restoring the value. But
> > > > then someone can say why do we allow enabling the PL1 limit since we
> > > > want to disable it.
> > > >
> > > > Both these are very unlikely scenarios so they might work. But I would
> > > > first like to explore if holding a mutex across GuC reset is prolebmatic
> > > > since that is /the/ correct solution. But if anyone comes up with a reason
> > > > why that cannot be done we can look at these other not completely correct
> > > > options.
> > >
> > > I see what you are doing and it looks indeed a very safe approach to ensure
> > > the pl1 won't be toggled by other paths while we need some guaranteed state
> > > here, or hw init fails badly.
> > >
> > > But in the end you are making your lock to protect the code from another path
> > > and not protecting the data itself. The data was already protected in the
> > > first version with the lock in the rmw.
> >
> > Sorry I am not really following. Daniel had mentioned this "protecting code
> > vs protecting data" but I am wondering how it is applicable in this
> > case. IMO here the data we are protecting is the register which we don't
> > want written to by userland while GuC load is in progress. To do that we
> > need to block the code path writing to register. So what we have here seems
> > to me to be the simplest and cleanest approach for solving this issue.
>
> I believe your cases here is exactly what Daniel had mentioned as protecting
> code and not data. Well, in the end we are of course protecting data to be
> modified, but in your case you use that mutex to also protect the code path
> and avoid other calls while you are in this guc_init_path...
>
> Please Daniel, correct me here if I got it wrong.
>
> What I don't like here is that we lock from one function and keep that for a
> while and unlock from the other function. To protect the data itself in general
> we just need for a very minimal time while we are modifying the data itself.
>
> >
> > > maybe we need to have some kind of a state check with other state-lock and
> > > then if we are in this forced state for init path, the request for the normal path
> > > ignores and move one,
> >
> > I don't see how this will *not* be racy...
>
> maybe something like this?:
>
> at power_max_disable:
> mutex_lock(data_lock);
>
> mutex_lock(state_lock);
> state = in_use;
> mutex_unlock(state_lock);
>
> mmio_rmw();
> mutex_unlock(data_lock);
>
>
> at power_max_restoration:
>
> at power_max_disable:
> mutex_lock(data_lock);
>
> mutex_lock(state_lock);
> state = available;
> mutex_unlock(state_lock);
>
> mmio_rmw();
> mutex_unlock(data_lock);
>
> at sysfs fn:
>
> mutex_lock(data_lock);
> mutex_lock(state_lock);
> if (state == in_use) {
> ret = -EAGAIN
> goto out;
> }
> mutex_unlock(state_lock);
>
> ....
>
> out:
>
> mutex_unlock(data_lock);
Thanks for suggesting this, actually it worked out quite nicely and I have
implemented this in the latest version.
Though I believe state_lock is not needed (data_lock is sufficient) so I
have skipped that. Please take a look at:
https://patchwork.freedesktop.org/series/116172/
Thanks.
--
Ashutosh
>
> >
> > > or maybe we queue some request...
> >
> > Queuing a request will not be enough (even if this is possible), the
> > request will need to wait to complete till GuC load completes. So we'll
> > have to complete the request when GuC load completes, similar to releasing
> > the mutex in the current patch. Looks like a much more complicated way of
> > doing what the mutex does very simply.
>
> The wq would sleep/delay while state == in_use, then process the next request...
>
> >
> > So:
> >
> > a. What is the real problem with the current implementation?
>
> probably the big lock used to protect the state machinery...
>
> but if other folks believe that we don't have an actual problem here
> and this big lock is acceptable as long as it has the annotation for
> the static analyzers, I'm okay to just let it go...
>
>
> >
> > b. What would be the correct solution for it? That is how, specifically,
> > should we implement it?
>
> state handling with separated lock from the data itself is my suggestion.
>
> >
> > Some more guidance will be helpful if you think this patch has issues.
>
> I hope Daniel and/or other i915 maintainers can jump here. Specially if
> I'm being to paranoid and the current patch is enough...
>
> >
> > Thanks.
> > --
> > Ashutosh
> >
> > > > ```
> > > >
> > > > > > +
> > > > > > + *old = !!(r & PKG_PWR_LIM_1_EN);
> > > > > > +}
> > > > > > +
> > > > > > +void i915_hwmon_power_max_restore(struct drm_i915_private *i915, bool old)
> > > > > > + __releases(i915->hwmon->hwmon_lock)
> > > > > We can just call this i915_hwmon_power_max_enable() and call whenever the
> > > > > old value was actually enabled. That way, we have proper mirror functions.
> > > >
> > > > As I explained that would mean adding two checks in the main __uc_init_hw()
> > > > function which I am trying to avoid. So we have disable/restore pair.
> > > >
> > > > > > +{
> > > > > > + struct i915_hwmon *hwmon = i915->hwmon;
> > > > > > + intel_wakeref_t wakeref;
> > > > > > +
> > > > > > + if (!hwmon || !i915_mmio_reg_valid(hwmon->rg.pkg_rapl_limit))
> > > > > > + return;
> > > > > > +
> > > > > > + with_intel_runtime_pm(hwmon->ddat.uncore->rpm, wakeref)
> > > > > > + intel_uncore_rmw(hwmon->ddat.uncore,
> > > > > > + hwmon->rg.pkg_rapl_limit,
> > > > > > + PKG_PWR_LIM_1_EN,
> > > > > > + old ? PKG_PWR_LIM_1_EN : 0);
> > > > >
> > > > > 3rd param should be 0 here, else we will end up clearing other bits.
> > > >
> > > > No see intel_uncore_rmw(), it will only clear the PKG_PWR_LIM_1_EN bit, so
> > > > the code here is correct. intel_uncore_rmw() does:
> > > >
> > > > val = (old & ~clear) | set;
> > > >
> > > > So for now I am not making any changes, if you feel strongly about
> > > > something one way or another let me know. Anyway these comments should help
> > > > you understand the patch better so take a look and we can go from there.
> > > >
> > > > Thanks.
> > > > --
> > > > Ashutosh
> > > >
> > > > > > +
> > > > > > + mutex_unlock(&hwmon->hwmon_lock);
> > > > > > +}
> > > > > > +
> > > > > > static umode_t
> > > > > > hwm_energy_is_visible(const struct hwm_drvdata *ddat, u32 attr)
> > > > > > {
> > > > > > diff --git a/drivers/gpu/drm/i915/i915_hwmon.h b/drivers/gpu/drm/i915/i915_hwmon.h
> > > > > > index 7ca9cf2c34c96..0fcb7de844061 100644
> > > > > > --- a/drivers/gpu/drm/i915/i915_hwmon.h
> > > > > > +++ b/drivers/gpu/drm/i915/i915_hwmon.h
> > > > > > @@ -7,14 +7,21 @@
> > > > > > #ifndef __I915_HWMON_H__
> > > > > > #define __I915_HWMON_H__
> > > > > > +#include <linux/types.h>
> > > > > > +
> > > > > > struct drm_i915_private;
> > > > > > +struct intel_gt;
> > > > > > #if IS_REACHABLE(CONFIG_HWMON)
> > > > > > void i915_hwmon_register(struct drm_i915_private *i915);
> > > > > > void i915_hwmon_unregister(struct drm_i915_private *i915);
> > > > > > +void i915_hwmon_power_max_disable(struct drm_i915_private *i915, bool *old);
> > > > > > +void i915_hwmon_power_max_restore(struct drm_i915_private *i915, bool old);
> > > > > > #else
> > > > > > static inline void i915_hwmon_register(struct drm_i915_private *i915) { };
> > > > > > static inline void i915_hwmon_unregister(struct drm_i915_private *i915) { };
> > > > > > +static inline void i915_hwmon_power_max_disable(struct drm_i915_private *i915, bool *old) { };
> > > > > > +static inline void i915_hwmon_power_max_restore(struct drm_i915_private *i915, bool old) { };
> > > > > > #endif
> > > > > > #endif /* __I915_HWMON_H__ */
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