linux-kernel - Re: [PATCH 07/10] cpu/SMT: Allow enabling partial SMT states via sysfs

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Date:   Thu, 22 Jun 2023 11:12:24 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Laurent Dufour <ldufour@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        npiggin@...il.com, christophe.leroy@...roup.eu,
        dave.hansen@...ux.intel.com, mingo@...hat.com, bp@...en8.de
Subject: Re: [PATCH 07/10] cpu/SMT: Allow enabling partial SMT states via sysfs

On Thu, Jun 15 2023 at 17:46, Laurent Dufour wrote:
>  
> -	if (ctrlval != cpu_smt_control) {
> +	orig_threads = cpu_smt_num_threads;
> +	cpu_smt_num_threads = num_threads;
> +
> +	if (num_threads > orig_threads) {
> +		ret = cpuhp_smt_enable();
> +	} else if (num_threads < orig_threads) {
> +		ret = cpuhp_smt_disable(ctrlval);
> +	} else if (ctrlval != cpu_smt_control) {
>  		switch (ctrlval) {
>  		case CPU_SMT_ENABLED:
>  			ret = cpuhp_smt_enable();

This switch() is still as pointless as in the previous version.

OFF -> ON, ON -> OFF, ON -> FORCE_OFF are covered by the num_threads
comparisons.

So the only case where (ctrlval != cpu_smt_control) is relevant is the
OFF -> FORCE_OFF transition because in that case the number of threads
is not changing.

          force_off = ctrlval != cpu_smt_control && ctrval == CPU_SMT_FORCE_DISABLED;

	  if (num_threads > orig_threads)
		  ret = cpuhp_smt_enable();
	  else if (num_threads < orig_threads || force_off)
		  ret = cpuhp_smt_disable(ctrlval);

Should just work, no?

Thanks,

        tglx