From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 269CFC7618F for ; Tue, 23 Jul 2019 02:43:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E952A2238C for ; Tue, 23 Jul 2019 02:43:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731316AbfGWCm7 (ORCPT ); Mon, 22 Jul 2019 22:42:59 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:2697 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726284AbfGWCm7 (ORCPT ); Mon, 22 Jul 2019 22:42:59 -0400 Received: from DGGEMS413-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 35986DA5A63EAACD6368; Tue, 23 Jul 2019 10:42:57 +0800 (CST) Received: from [127.0.0.1] (10.177.223.23) by DGGEMS413-HUB.china.huawei.com (10.3.19.213) with Microsoft SMTP Server id 14.3.439.0; Tue, 23 Jul 2019 10:42:55 +0800 Subject: Re: [PATCH 0/3] arm64: Allow early timestamping of kernel log To: Marc Zyngier , Thomas Gleixner , John Stultz , Pavel Tatashin , Petr Mladek , "Sergey Senozhatsky" , Steven Rostedt , Will Deacon , Catalin Marinas , Mark Rutland CC: , References: <20190722103330.255312-1-marc.zyngier@arm.com> From: Hanjun Guo Message-ID: <83634882-a528-a05d-f38c-cd0f58d1e6ee@huawei.com> Date: Tue, 23 Jul 2019 10:42:15 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20190722103330.255312-1-marc.zyngier@arm.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.223.23] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/7/22 18:33, Marc Zyngier wrote: > So far, we've let the arm64 kernel start its meaningful time stamping > of the kernel log pretty late, which is caused by sched_clock() being > initialised rather late compared to other architectures. > > Pavel Tatashin proposed[1] to move the initialisation of sched_clock > much earlier, which I had objections to. The reason for initialising > sched_clock late is that a number of systems have broken counters, and > we need to apply all kind of terrifying workarounds to avoid time > going backward on the affected platforms. Being able to identify the > right workaround comes pretty late in the kernel boot, and providing > an unreliable sched_clock, even for a short period of time, isn't an > appealing prospect. > > To address this, I'm proposing that we allow an architecture to chose > to (1) divorce time stamping and sched_clock during the early phase of > booting, and (2) inherit the time stamping clock as the new epoch the > first time a sched_sched clock gets registered. > > (1) would allow arm64 to provide a time stamping clock, however > unreliable it might be, while (2) would allow sched_clock to provide > time stamps that are continuous with the time-stamping clock. > > The last patch in the series adds the necessary logic to arm64, > allowing the (potentially unreliable) time stamping of early kernel > messages. > > Tested on a bunch of arm64 systems, both bare-metal and in VMs. Boot > tested on a x86 guest. This makes the boot log more useful and I can debug some time consuming issue easier before the arch timer initialization, tested on my ARM64 server, I can see the timestamping from the start [1], Tested-by: Hanjun Guo Thanks Hanjun [1]: [ 0.000000] Booting Linux on physical CPU 0x0000080000 [0x481fd010] [ 0.000000] Linux version 5.2.0+ (root@localhost.localdomain) (gcc version 9.0.1 20190312 (Red Hat 9.0.1-0.10) (GCC)) #45 SMP Tue Jul 23 09:17:48 CST 2019 [ 0.000000] Using timestamp clock @100MHz [ 0.000074] efi: Getting EFI parameters from FDT: [ 0.000082] efi: EFI v2.70 by EDK II [ 0.000083] efi: ACPI 2.0=0x3a300000 SMBIOS 3.0=0x39f80000 MEMATTR=0x30996018 MEMRESERVE=0x30997e18 [ 0.000122] crashkernel reserved: 0x000000000ba00000 - 0x000000002ba00000 (512 MB) [ 0.000126] cma: Failed to reserve 512 MiB [ 0.185111] ACPI: Early table checksum verification disabled [ 0.185115] ACPI: RSDP 0x000000003A300000 000024 (v02 HISI ) [ 0.185120] ACPI: XSDT 0x000000003A270000 00009C (v01 HISI HIP08 00000000 01000013) [ 0.185127] ACPI: FACP 0x0000000039B10000 000114 (v06 HISI HIP08 00000000 HISI 20151124) [ 0.185134] ACPI: DSDT 0x0000000039AB0000 0084E4 (v02 HISI HIP08 00000000 INTL 20181213) [ 0.185139] ACPI: PCCT 0x0000000039FB0000 00008A (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185143] ACPI: SSDT 0x0000000039F90000 01021A (v02 HISI HIP07 00000000 INTL 20181213) [ 0.185147] ACPI: BERT 0x0000000039F50000 000030 (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185150] ACPI: HEST 0x0000000039F30000 000308 (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185154] ACPI: ERST 0x0000000039EF0000 000230 (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185158] ACPI: EINJ 0x0000000039EE0000 000170 (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185162] ACPI: SLIT 0x0000000039B30000 00003C (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185166] ACPI: GTDT 0x0000000039B00000 00007C (v02 HISI HIP08 00000000 HISI 20151124) [ 0.185169] ACPI: MCFG 0x0000000039AF0000 00003C (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185173] ACPI: SPCR 0x0000000039AE0000 000050 (v02 HISI HIP08 00000000 HISI 20151124) [ 0.185177] ACPI: SRAT 0x0000000039AD0000 0007D0 (v03 HISI HIP08 00000000 HISI 20151124) [ 0.185181] ACPI: APIC 0x0000000039AC0000 001E6C (v04 HISI HIP08 00000000 HISI 20151124) [ 0.185185] ACPI: IORT 0x0000000039AA0000 001310 (v00 HISI HIP08 00000000 INTL 20181213) [ 0.185189] ACPI: PPTT 0x0000000030970000 0031B0 (v01 HISI HIP08 00000000 HISI 20151124) [ 0.185196] ACPI: SPCR: console: pl011,mmio32,0x94080000,115200 [ 0.185208] ACPI: SRAT: Node 0 PXM 0 [mem 0x2080000000-0x2fffffffff] [ 0.185210] ACPI: SRAT: Node 1 PXM 1 [mem 0x3000000000-0x3fffffffff] [ 0.185212] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x7fffffff] [ 0.185213] ACPI: SRAT: Node 2 PXM 2 [mem 0x202000000000-0x202fffffffff] [ 0.185215] ACPI: SRAT: Node 3 PXM 3 [mem 0x203000000000-0x203fffffffff] [ 0.185221] NUMA: NODE_DATA [mem 0x2fffffe3c0-0x2fffffffff] [ 0.185224] NUMA: NODE_DATA [mem 0x3fffffe3c0-0x3fffffffff] [ 0.185226] NUMA: NODE_DATA [mem 0x202fffffe3c0-0x202fffffffff] [ 0.185229] NUMA: NODE_DATA [mem 0x203ffdfde3c0-0x203ffdfdffff]