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-----Original Message----- From: Dave Hansen dave.hansen@intel.com Sent: Thursday, September 22, 2022 13:18 To: Limonciello, Mario Mario.Limonciello@amd.com; Nayak, K Prateek KPrateek.Nayak@amd.com; linux-kernel@vger.kernel.org Cc: rafael@kernel.org; lenb@kernel.org; linux-acpi@vger.kernel.org; linux- pm@vger.kernel.org; dave.hansen@linux.intel.com; bp@alien8.de; tglx@linutronix.de; andi@lisas.de; puwen@hygon.cn; peterz@infradead.org; rui.zhang@intel.com; gpiccoli@igalia.com; daniel.lezcano@linaro.org; Narayan, Ananth Ananth.Narayan@amd.com; Shenoy, Gautham Ranjal gautham.shenoy@amd.com; Ong, Calvin Calvin.Ong@amd.com; stable@vger.kernel.org; regressions@lists.linux.dev Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors based on the Zen microarchitecture
On 9/22/22 10:48, Limonciello, Mario wrote:
- The title says to limit it to old intel systems, but nothing about this
actually enforces that.
It actually is limited to all Intel systems, but effectively won't be used on
anything but new
ones because of intel_idle.
As an idea for #2 you could check for CONFIG_INTEL_IDLE in the Intel case
and
if it's not defined show a pr_notice_once() type of message trying to tell
people to use
Intel Idle instead for better performance.
What does that have to do with *this* patch, though?
It was just a thought triggered by your commit message title.
If you've got CONFIG_INTEL_IDLE disabled, you'll be slow before this patch. You'll also be slow after this patch. It's entirely orthogonal.
Yeah it's orthogonal, but with this discussion happening and the code is changing /anyway/ then a pr_notice_once() seemed like a nice way to guide people towards intel_idle at the same time so they didn't trip into the same problem AMD systems do today.
I can add a "Practically" to the subject so folks don't confuse it with some hard limit that is being enforced:
ACPI: processor idle: Practically limit "Dummy wait" workaround to old Intel systems
That works.
BTW, is there seriously a strong technical reason that AMD systems are still using this code? Or is it pure inertia?
Maybe a better question for Ananth and Prateek to comment on.