Re: [PATCH] rcu/nocb: Keep lazy timer intact on second lazy callback

[Joel Fernandes]

On chriswiseman@xxxxxxxxxx wrote:
> Hi Joel,
> 
> > Looks reasonable to me. Is there a test case that you added to find this, or any
> > power savings that you found with this added patch?
> 
> I spotted this while tracing idle rcuog wakeups with CONFIG_RCU_LAZY=y
> and rcu_nocbs=all, where rcuog kept waking up after 1 jiffy whenever a
> second CPU in the group queued a lazy callback.  I verified it with
> rcutorture (NOCB01) and measured a light background callback workload on
> an arm64 system:
> 
>                         Before          After           Delta
> rcuog wakeups:          1,885           1,174           -37.7%
> 1-jiffy timer resets:     739               0          -100.0%
> SoC power (CPU+DSU):   94.1 mW         76.5 mW          -18.6% (-17.5 mW)
> 

Looks nice! I will apply the patch and run some tests.

Reviewed-by: Joel Fernandes <jfern@xxxxxxxxxx>

> Thanks,
> Chris