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Re: [PATCH 1/6] powernv:idle: Correctly initialize core_idle_state_ptr

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  Re: [PATCH 1/6] powernv:idle: Correctly initialize  core_idle_state_ptr Nicholas Piggin <npiggin@gmail.com> - 2017-05-30 08:00 +0200
    Re: [PATCH 1/6] powernv:idle: Correctly initialize  core_idle_state_ptr Gautham R Shenoy <ego@linux.vnet.ibm.com> - 2017-05-30 12:30 +0200

#1652820 — Re: [PATCH 1/6] powernv:idle: Correctly initialize core_idle_state_ptr

On Tue, 16 May 2017 14:19:43 +0530
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> wrote:

> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> 
> The lower 8 bits of core_idle_state_ptr tracks the number of non-idle
> threads in the core. This is supposed to be initialized to bit-map
> corresponding to the threads_per_core. However, currently it is
> initialized to PNV_CORE_IDLE_THREAD_BITS (0xFF). This is correct for
> POWER8 which has 8 threads per core, but not for POWER9 which has 4
> threads per core.
> 
> As a result, on POWER9, core_idle_state_ptr gets initialized to
> 0xFF. In case when all the threads of the core are idle, the bits
> corresponding tracking the idle-threads are non-zero. As a result, the
> idle entry/exit code fails to save/restore per-core hypervisor state
> since it assumes that there are threads in the cores which are still
> active.
> 
> Fix this by correctly initializing the lower bits of the
> core_idle_state_ptr on the basis of threads_per_core.
> 
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

This looks good to me.

Until this patch series, we can't enable HV state loss idle modes
on POWER9, is that correct? And after your series does it work?

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

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#1653080

Hi Nicholas,

On Tue, May 30, 2017 at 03:56:12PM +1000, Nicholas Piggin wrote:
> On Tue, 16 May 2017 14:19:43 +0530
> "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> wrote:
> 
> > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> > 
> > The lower 8 bits of core_idle_state_ptr tracks the number of non-idle
> > threads in the core. This is supposed to be initialized to bit-map
> > corresponding to the threads_per_core. However, currently it is
> > initialized to PNV_CORE_IDLE_THREAD_BITS (0xFF). This is correct for
> > POWER8 which has 8 threads per core, but not for POWER9 which has 4
> > threads per core.
> > 
> > As a result, on POWER9, core_idle_state_ptr gets initialized to
> > 0xFF. In case when all the threads of the core are idle, the bits
> > corresponding tracking the idle-threads are non-zero. As a result, the
> > idle entry/exit code fails to save/restore per-core hypervisor state
> > since it assumes that there are threads in the cores which are still
> > active.
> > 
> > Fix this by correctly initializing the lower bits of the
> > core_idle_state_ptr on the basis of threads_per_core.
> > 
> > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> 
> This looks good to me.
> 
> Until this patch series, we can't enable HV state loss idle modes
> on POWER9, is that correct? And after your series does it work?

Yes, that is correct.

> 
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
>

Thanks for reviewing the patch!

--
Thanks and Regards
gautham.

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