linux-kernel - Re: [PATCH 1/6] powernv:idle: Correctly initialize core_idle_state

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Date:   Tue, 30 May 2017 15:56:12 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: 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@...ux.vnet.ibm.com> wrote:

> From: "Gautham R. Shenoy" <ego@...ux.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@...ux.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@...il.com>