[PATCH] powerpc/pseries: fix accuracy of stolen time

[Srikar Dronamraju]

* Shrikanth Hegde <sshegde at linux.ibm.com> [2024-02-13 10:56:35]:

> powerVM hypervisor updates the VPA fields with stolen time data.
> It currently reports enqueue_dispatch_tb and ready_enqueue_tb for
> this purpose. In linux these two fields are used to report the stolen time.
> 
> The VPA fields are updated at the TB frequency. On powerPC its mostly
> set at 512Mhz. Hence this needs a conversion to ns when reporting it
> back as rest of the kernel timings are in ns. This conversion is already
> handled in tb_to_ns function. So use that function to report accurate
> stolen time.
> 
> Observed this issue and used an Capped Shared Processor LPAR(SPLPAR) to
> simplify the experiments. In all these cases, 100% VP Load is run using
> stress-ng workload. Values of stolen time is in percentages as reported
> by mpstat. With the patch values are close to expected.
> 
> 		6.8.rc1		+Patch
> 12EC/12VP	   0.0		   0.0
> 12EC/24VP	  25.7		  50.2
> 12EC/36VP	  37.3		  69.2
> 12EC/48VP	  38.5		  78.3
> 
> 
> Fixes: 0e8a63132800 ("powerpc/pseries: Implement CONFIG_PARAVIRT_TIME_ACCOUNTING")
> Signed-off-by: Shrikanth Hegde <sshegde at linux.ibm.com>

Looks good to me.

Reviewed-by: Srikar Dronamraju <srikar at linux.vnet.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju