Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 26 Oct 2022 11:32:27 +0800
From:   Fei Li <fei1.li@intel.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
        <dave.hansen@intel.com>, <gregkh@linuxfoundation.org>,
        <tglx@linutronix.de>, <mingo@redhat.com>, <bp@alien8.de>,
        <dave.hansen@linux.intel.com>, <hpa@zytor.com>,
        <Yu1.Wang@intel.com>, <conghui.chen@intel.com>,
        <fengwei.yin@intel.com>
Subject: Re: [PATCH] x86/acrn: Set X86_FEATURE_TSC_KNOWN_FREQ
Message-ID: <Y1iqS3FuCjPE8icm@louislifei-OptiPlex-7090>
References: <20221025084147.4118463-1-fei1.li@intel.com>
 <Y1fjMnX9UOVo2+K5@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <Y1fjMnX9UOVo2+K5@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?9+3G0LzlEklvmsFXIVO4soVLNu54sRHKWdltkrSsrcLimQnp6Vg0TfbNqBce?=
 =?us-ascii?Q?40Pq+s9/krUexIbYnlUIao0cs9Cr9t8MCPGhB5aRdbZ7r9cdj8j4jkYOdiuU?=
 =?us-ascii?Q?NQD4f9wXroRf6ihxdTWHlrn/Hcsu53q8N0WBLSTqhA438Mn8k5+mhTXCqZCB?=
 =?us-ascii?Q?urKUyF4k7e1C4I2svK8h8tHuTnU0R6klTXyT9PXto7tA7qlXbCTb8zHbF43g?=
 =?us-ascii?Q?qwIw0SplvmnYJ/yz1DTumTILijUeWEcl/z9GdnpdKm5FMolppghV88H7q/Sp?=
 =?us-ascii?Q?+MFyqFymlfeOlFB9c5CG16oDs2w+zxSmoyCw1oGJ/mpn9sqqWKFzd3+3cDAs?=
 =?us-ascii?Q?IwazR3QzyQBAnxkctRLsw8Sval1/JekgZo7RT2NuWK6O9ds+Yi0indjaA/T6?=
 =?us-ascii?Q?O78+jkdeSDir7R779wTkKwTmJsVfqe04EX9NnxhYspWEFJB41IAApAqF5SyM?=
 =?us-ascii?Q?g3vzR6jOf+k4xclKN8T92Ah7/7ciZJs5DHDLBPVWCi5pVzA9sHhSv/KmDMLg?=
 =?us-ascii?Q?Zq3k7Moh2JKtQDq/vBhhz4iXCrLeHgece5QuPUMaYnd4Qf2HLSO9G65F/cqc?=
 =?us-ascii?Q?f5SRdzd2IVkeTV76wVl5Yt8TR/8ZHI53GzDgVAdk0taWgbNp6WboxrjvuSvw?=
 =?us-ascii?Q?6X9ExHIalZ/frdF8kCrOpVEWYp//XTGxF6YBZx8MQ32sL5qwaWyJrnP4d4if?=
 =?us-ascii?Q?IXNmHtySIbqSkVvsxFFu8sJDvpgsI1SFCBcXRq03ko4NLE3UQ4wss04t51S1?=
 =?us-ascii?Q?MfDolHZXKoHBcAKnONXBvDtU413i+C+2NkH/otzf1R4yRIkQLN0wFfkqhzBA?=
 =?us-ascii?Q?CMgYlx6pGzk1zrIgY2cNeE5oagSirTrVVyQpQQtjW6dooqyMiNiVYUd7vYfI?=
 =?us-ascii?Q?x3tqUlATYU3OD/IQBFBKNQnFkZ5xO68+6KEhEAz+tPDVbYzszCNk9ZHgHE8W?=
 =?us-ascii?Q?WqGGgcCTCFNwrDJBX8QcZU5bkGtzfvydNPmJ6z+otNlhinyLnppQR7sSLTtt?=
 =?us-ascii?Q?OuEFvckggVlxzbBAPva1V4kz9Lt4ROUKZZKo0IQ8LlfQjt+o2TVNzPJ38W3k?=
 =?us-ascii?Q?FKmERJsObgh/LW3zAVG+RD8ffRNnX5bYOhsT7i65eIRMGvc1CdRqBvCjgEKW?=
 =?us-ascii?Q?AyLLDqYlxUFZYET8WuLESWvBhWapMWbBqKuyoWDiyYF/7xbO6cUiJJoHOf2E?=
 =?us-ascii?Q?cf297O1KEPL5kHfEEbHa/qqWruRP3LMDyLBKp2OK2NygiGyquzhyZz8yQKiZ?=
 =?us-ascii?Q?d6YSGBvbnCaaHIIytC6ba/Z9VWXO56OrF9wdc+U73h6o76jD6Lba3c99HQAR?=
 =?us-ascii?Q?6Ead8cmaxHNn1zf9wq5PkRXDsRq5vPIzmSbM/LRslRliLgfJ6ja70DRC9/Cl?=
 =?us-ascii?Q?y5s0aQ8KqVH9QRaTY0hFYC04GE5+dQopUb5W6CDW4q9m3gaNIn6WrmvFOJBI?=
 =?us-ascii?Q?wyp1mdqxvSSDAFxchAkmNpzCtRDwt652nlAMK9ofoDCuWC6pUtIXY2ndGcDC?=
 =?us-ascii?Q?1sL/TTgsgHWZTgfnpybTZ2Rq3j6OhERJ+oFfqYUphitAhd9llzllQUzSyBxe?=
 =?us-ascii?Q?WNHQADOqRwUiwn/+xLtSD8a7U9ImlswcnZMBabrz?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 8726656f-205c-49ee-bcdb-08dab701e707
X-MS-Exchange-CrossTenant-AuthSource: SJ1PR11MB6153.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Oct 2022 03:26:42.6178
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 3Cuf7ulnSnQOKKUEDhOEBbg5ED7XQann+7Q77XMXApwKm+QPabsudXdyfat2NqWByxav7FG7QqKVS0yhIe3fiw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA2PR11MB4826
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,
        SPF_NONE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 2022-10-25 at 15:22:58 +0200, Peter Zijlstra wrote:
> On Tue, Oct 25, 2022 at 04:41:47PM +0800, Fei Li wrote:
> > Avoiding recalibration by setting X86_FEATURE_TSC_KNOWN_FREQ.
> > This patch also removes `inline` for acrn_get_tsc_khz() since
> > it doesn't make sense.
> 
Hi Peter

Thanks for your comments.

> Can we have a few words on how this is supposed to work at all?

If the TSC frequency is known from the acrn_get_tsc_khz(),
the TSC frequency does not need to be recalibrated.

We can avoid recalibration by setting X86_FEATURE_TSC_KNOWN_FREQ.
> 
> Supposedly the HV is providing host rate through this ACRN CPUID leaf?
ACRN would provide the calibrated TSC frequency, not just the
host rate through this CPUID leaf.

> How does it deal with systems where TSC isn't known stable?
>