From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id CDF382561
	for <regressions@lists.linux.dev>; Fri, 23 Sep 2022 07:58:29 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
	d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version:
	References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:
	Content-Transfer-Encoding:Content-ID:Content-Description;
	bh=OBb/Vyt/knoHoeVbmT/onk2LeOhkHBZeeIy4HQ7B610=; b=kbx8x+vJdxxg0SYtDk6TZ/8TQ0
	LRgsxJZK09kxU4gmM2WloCSBDUu4eSWhSD4GWQXXHQTmkESIqSLqInRQCVl+N98wZqz+lvMK7Gohh
	lGEaPydkRwFl0hvrvnc+OAIp1oT07orwd6jaiouTzuYj/o9bd1VflVdaf42S50eCYqBtezEK8N0qB
	EI85G4Dzlkg1aWZSVGWmcNplNbVOrJ6Gfn8Fsc8VQexstnwQamqQOirbg+SSMQm1Q4sAIf/3f9NPW
	lAt1/dKXB7IKFHQLKijTg+0jw5jLSlunoSIHlGlrfgB0hGHgaXQKHv5Ta7qMhuv5en7RHhWppGVK/
	E6EC9rYA==;
Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net)
	by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux))
	id 1obdZI-00FAQd-33; Fri, 23 Sep 2022 07:57:54 +0000
Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225])
	(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
	 key-exchange X25519 server-signature RSA-PSS (4096 bits))
	(Client did not present a certificate)
	by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 386193001FD;
	Fri, 23 Sep 2022 09:57:51 +0200 (CEST)
Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000)
	id 1970C207C83B0; Fri, 23 Sep 2022 09:57:51 +0200 (CEST)
Date: Fri, 23 Sep 2022 09:57:51 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andreas Mohr <andi@lisas.de>, K Prateek Nayak <kprateek.nayak@amd.com>,
	linux-kernel@vger.kernel.org, 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,
	puwen@hygon.cn, mario.limonciello@amd.com, rui.zhang@intel.com,
	gpiccoli@igalia.com, daniel.lezcano@linaro.org,
	ananth.narayan@amd.com, gautham.shenoy@amd.com,
	Calvin Ong <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
Message-ID: <Yy1m/5topydhbWS2@hirez.programming.kicks-ass.net>
References: <20220921063638.2489-1-kprateek.nayak@amd.com>
 <20e78a49-25df-c83d-842e-1d624655cfd7@intel.com>
 <0885eecb-042f-3b74-2965-7d657de59953@amd.com>
 <88c17568-8694-940a-0f1f-9d345e8dcbdb@intel.com>
 <Yyy6l94G0O2B7Yh1@rhlx01.hs-esslingen.de>
 <YyzBLc+OFIN2BMz5@rhlx01.hs-esslingen.de>
 <4d61b9c0-ee00-c5f6-bef1-622b80c79714@intel.com>
Precedence: bulk
X-Mailing-List: regressions@lists.linux.dev
List-Id: <regressions.lists.linux.dev>
List-Subscribe: <mailto:regressions+subscribe@lists.linux.dev>
List-Unsubscribe: <mailto:regressions+unsubscribe@lists.linux.dev>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4d61b9c0-ee00-c5f6-bef1-622b80c79714@intel.com>

On Thu, Sep 22, 2022 at 02:21:31PM -0700, Dave Hansen wrote:
> FWIW, I'd much rather do something like
> 
> 	if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
> 	    (boot_cpu_data.x86_model >= 0xF))
> 		return;
> 
> 	inl(slow_whatever);
> 
> than a Zen check.  AMD has, as far as I know, been a lot more sequential
> and sane about model numbers than Intel, and there are some AMD model
> number range checks in the codebase today.

Some might be broken; apparently their SoC/Entertainment divisions has a
few out of order SKUs that were not listed in their regular documents.
(yay interweb)

I ran into this when I tried doing a Zen2 range check for retbleed. In
the end we ended up using the availablility of STIBP as a heuristic to
indentify Zen2+ or something.