Re: [PATCH v3 10/15] cpufreq/amd-pstate: Move limit updating code
From: Mario Limonciello
Date: Mon Dec 16 2024 - 10:40:40 EST
On 12/16/2024 08:45, Dhananjay Ugwekar wrote:
On 12/16/2024 7:51 PM, Mario Limonciello wrote:
On 12/16/2024 08:16, Dhananjay Ugwekar wrote:
Hello Mario,
On 12/10/2024 12:22 AM, Mario Limonciello wrote:
The limit updating code in amd_pstate_epp_update_limit() should not
only apply to EPP updates. Move it to amd_pstate_update_min_max_limit()
so other callers can benefit as well.
With this move it's not necessary to have clamp_t calls anymore because
the verify callback is called when setting limits.
While testing this series, I observed that with amd_pstate=passive + schedutil governor,
the scaling_max_freq limits were not being honored and I bisected the issue down to this
patch.
I went through the code and noticed that in amd_pstate_adjust_perf(), we set the min_perf
field in MSR_AMD_CPPC_REQ to "cap_perf" which is equal to cpudata->highest_perf (which is
equal to 255 for non-preferred cores systems). This didnt seem logical to me and I changed
cap_perf to cpudata->max_limit_perf which gives us the value updated in scaling_max_freq.
I think as we removed the redundant clamping code, this pre-existing issue got exposed.
The below diff fixes the issue for me.
Please let me know your thoughts on this.
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index d7b1de97727a..1ac34e3f1fc5 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -699,7 +699,7 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
if (min_perf < lowest_nonlinear_perf)
min_perf = lowest_nonlinear_perf;
here^^^
- max_perf = cap_perf;
+ max_perf = cpudata->max_limit_perf;
if (max_perf < min_perf)
max_perf = min_perf;
With this change I think you can also drop the comparison afterwards, as an optimization right?
Umm I think it is possible that scaling_max_freq is set to a value lower than
lowest_nonlinear_freq in that case this if condition would be needed (as min_perf
is being lower bounded at lowest_nonlinear_freq at the location highlighted above).
I would be okay with keeping this check in.
Well this feels like a bigger problem actually - why is it forcefully
bounded at lowest nonlinear freq? Performance is going to be awful at
that level (hence why commit 5d9a354cf839a ("cpufreq/amd-pstate: Set the
initial min_freq to lowest_nonlinear_freq") was done),
but shouldn't we "let" people go below that in passive and guided? We
do for active.
Also, what is the behavior if max_perf is set to a value lower than min_perf in
the CPPC_REQ MSR? I guess platform FW would also be smart enough to handle this
implicitly, but cant say for sure.
I would hope so too; but yeah you're right we don't know for sure.
As this is already in superm1.git/linux-next after testing can you please send a patch relative to superm1.git/linux-next branch?
Sure, I'll send out the patch once we finalize on the above if condition.
Regards,
Dhananjay
Thanks!
Thanks,
Dhananjay
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@xxxxxxx>
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
v2:
* Drop lowest_perf variable
---
drivers/cpufreq/amd-pstate.c | 28 +++++-----------------------
1 file changed, 5 insertions(+), 23 deletions(-)
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 3a3df67c096d5..dc3c45b6f5103 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -537,10 +537,6 @@ static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
u32 nominal_perf = READ_ONCE(cpudata->nominal_perf);
u64 value = prev;
- min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
- cpudata->max_limit_perf);
- max_perf = clamp_t(unsigned long, max_perf, cpudata->min_limit_perf,
- cpudata->max_limit_perf);
des_perf = clamp_t(unsigned long, des_perf, min_perf, max_perf);
max_freq = READ_ONCE(cpudata->max_limit_freq);
@@ -607,7 +603,7 @@ static int amd_pstate_verify(struct cpufreq_policy_data *policy_data)
static int amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
{
- u32 max_limit_perf, min_limit_perf, lowest_perf, max_perf, max_freq;
+ u32 max_limit_perf, min_limit_perf, max_perf, max_freq;
struct amd_cpudata *cpudata = policy->driver_data;
max_perf = READ_ONCE(cpudata->highest_perf);
@@ -615,12 +611,8 @@ static int amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
max_limit_perf = div_u64(policy->max * max_perf, max_freq);
min_limit_perf = div_u64(policy->min * max_perf, max_freq);
- lowest_perf = READ_ONCE(cpudata->lowest_perf);
- if (min_limit_perf < lowest_perf)
- min_limit_perf = lowest_perf;
-
- if (max_limit_perf < min_limit_perf)
- max_limit_perf = min_limit_perf;
+ if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
+ min_limit_perf = min(cpudata->nominal_perf, max_limit_perf);
WRITE_ONCE(cpudata->max_limit_perf, max_limit_perf);
WRITE_ONCE(cpudata->min_limit_perf, min_limit_perf);
@@ -1562,28 +1554,18 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
{
struct amd_cpudata *cpudata = policy->driver_data;
- u32 max_perf, min_perf;
u64 value;
s16 epp;
- max_perf = READ_ONCE(cpudata->highest_perf);
- min_perf = READ_ONCE(cpudata->lowest_perf);
amd_pstate_update_min_max_limit(policy);
- max_perf = clamp_t(unsigned long, max_perf, cpudata->min_limit_perf,
- cpudata->max_limit_perf);
- min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
- cpudata->max_limit_perf);
value = READ_ONCE(cpudata->cppc_req_cached);
- if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
- min_perf = min(cpudata->nominal_perf, max_perf);
-
value &= ~(AMD_CPPC_MAX_PERF_MASK | AMD_CPPC_MIN_PERF_MASK |
AMD_CPPC_DES_PERF_MASK);
- value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, max_perf);
+ value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, cpudata->max_limit_perf);
value |= FIELD_PREP(AMD_CPPC_DES_PERF_MASK, 0);
- value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, min_perf);
+ value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, cpudata->min_limit_perf);
/* Get BIOS pre-defined epp value */
epp = amd_pstate_get_epp(cpudata, value);