Re: [PATCH v3 1/2] cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged

On 26/09/2024 14:07, lihuisong (C) wrote:

在 2024/9/26 10:57, Jie Zhan 写道:

quoted

On 25/09/2024 17:28, lihuisong (C) wrote:

quoted

Hi Jie,

LGTM except for some trivial,
Reviewed-by: Huisong Li <lihuisong@huawei.com>

Thanks.

quoted

在 2024/9/19 16:45, Jie Zhan 写道:

quoted

The CPPC performance feedback counters could be 0 or unchanged when the
target cpu is in a low-power idle state, e.g. power-gated or clock-gated.

When the counters are 0, cppc_cpufreq_get_rate() returns 0 KHz, which makes
cpufreq_online() get a false error and fail to generate a cpufreq policy.

When the counters are unchanged, the existing cppc_perf_from_fbctrs()
returns a cached desired perf, but some platforms may update the real
frequency back to the desired perf reg.

For the above cases in cppc_cpufreq_get_rate(), get the latest desired perf
to reflect the frequency; if failed, return the cached desired perf.

Fixes: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
Reviewed-by: Zeng Heng <redacted>
Reviewed-by: Ionela Voinescu <redacted>
---
   drivers/cpufreq/cppc_cpufreq.c | 49 +++++++++++++++++++++++++++-------
   1 file changed, 39 insertions(+), 10 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index bafa32dd375d..e55192303a9f 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c

@@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work)

         perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs,
                        &fb_ctrs);
+    if (!perf)
+        return;
+
       cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
         perf <<= SCHED_CAPACITY_SHIFT;

@@ -726,11 +729,26 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,

         /* Check to avoid divide-by zero and invalid delivered_perf */

Now this comment can be removed, right?

Didn't notice this comment, but, having a check, I think it still fits.
'!delta_reference' avoids divide-by zero, and '!delta_delivered' checks
invalid delivered_perf.

The comment  "avoid divide-by zero" is just for the below code: "(reference_perf * delta_delivered) / delta_reference".
So It is also useful, but I think It's obvious and it doesn't make much sense.

The comment "avoid invalid delivered_perf" is for the return value.
Now this func return zero which can't count as a valid delivered_perf, right?

so, what about this?

/*
 * Avoid divide-by zero and unchanged feedback counters.
 * Leave it for callers to handle.
 */

quoted

So I think we just leave it unchanged.

...