Subject: Re: [PATCH v4] powerpc/64s: reimplement book3s idle code in C

From: Akshay Adiga <[email-masked]>
Date: Wed, 26 Sep 2018 19:39:14 +0530

On Fri, Sep 14, 2018 at 11:52:40AM +1000, Nicholas Piggin wrote:
> +
> +	/*
> +	 * On POWER9, SRR1 bits do not match exactly as expected.
> +	 * SRR1_WS_GPRLOSS (10b) can also result in SPR loss, so
> +	 * always test PSSCR if there is any state loss.
> +	 */
> +	if (likely((psscr & PSSCR_RL_MASK) < pnv_first_hv_loss_level)) {

Shouldn't we check PLS field to see if the cpu/core woke up from hv loss ?

Currently, a cpu requested stop4 (RL=4) and exited from a shallower state
(PLS=2), SPR's are unecessarily restored.

We can do something like : 

#define	PSSCR_PLS_SHIFT		60
if (likely((psscr & PSSCR_PLS) >> PSSCR_PLS_SHIFT) < pnv_first_hv_loss_level)
> +		if (sprs_saved)
> +			atomic_stop_thread_idle();
> +		goto out;
> +	}
> +
> +	/* HV state loss */
> +	BUG_ON(!sprs_saved);
> +
> +	atomic_lock_thread_idle();
> +
> +	if ((*state & ((1 << threads_per_core) - 1)) != 0)
> +		goto core_woken;
> +
> +	/* Per-core SPRs */
> +	mtspr(SPRN_PTCR,	sprs.ptcr);
> +	mtspr(SPRN_RPR,		sprs.rpr);
> +	mtspr(SPRN_TSCR,	sprs.tscr);
> +	mtspr(SPRN_LDBAR,	sprs.ldbar);
> +	mtspr(SPRN_AMOR,	sprs.amor);
> +
> +	if ((psscr & PSSCR_RL_MASK) >= pnv_first_tb_loss_level) {
> +		/* TB loss */
> +		if (opal_resync_timebase() != OPAL_SUCCESS)
> +			BUG();
> +	}