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Peter Anvin" , Peter Zijlstra , x86@kernel.org, linux-kernel@vger.kernel.org Cc: rui.zhang@intel.com, tim.c.chen@intel.com, Xiongfeng Wang , Feng Tang , Yu Liao Subject: [PATCH v2] x86/tsc: Extend watchdog check exemption to 4-Sockets platform Date: Thu, 13 Oct 2022 21:12:00 +0800 Message-Id: <20221013131200.973649-1-feng.tang@intel.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE, SPF_NONE 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: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1746578702566517070?= X-GMAIL-MSGID: =?utf-8?q?1746578702566517070?= There is report again that the tsc clocksource on a 4 sockets x86 Skylake server was wrongly judged as 'unstable' by 'jiffies' watchdog, and disabled [1]. Commit b50db7095fe0 ("x86/tsc: Disable clocksource watchdog for TSC on qualified platorms") was introduce to deal with these false alarms of tsc unstable issues, covering qualified platforms for 2 sockets or smaller ones. Extend the exemption to 4 sockets to fix the issue. We also got similar reports on 8 sockets platform from internal test, but as Peter pointed out, there was tsc sync issues for 8-sockets platform, and it'd better be handled architecture by architecture, instead of directly changing the threshold to 8 here. Rui also proposed another way to disable 'jiffies' as clocksource watchdog [2], which can also solve this specific problem in an architecture independent way, with one limitation that some tsc false alarms are reported by other watchdogs like HPET in post-boot time, while 'jiffies' is mostly used in boot phase before hardware clocksources are initialized. [1]. https://lore.kernel.org/all/9d3bf570-3108-0336-9c52-9bee15767d29@huawei.com/ [2]. https://lore.kernel.org/all/bd5b97f89ab2887543fc262348d1c7cafcaae536.camel@intel.com/ Reported-by: Yu Liao Tested-by: Yu Liao Signed-off-by: Feng Tang --- Hi reviewers: In the v1 review cycle, Dave raised the issue that 'nr_online_nodes' is not accurate, and could have problem with fakenuma (numa=fake=4 in cmdline) case and system with CPU-less HBM/PMEM nodes, which we have discussed in https://lore.kernel.org/lkml/Y0UgeUIJSFNR4mQB@feng-clx/ and will post the solution as a separate RFC patch. Thanks, Feng Changelog: Since v1: * Change the max socket number from 8 to 4, as Peter Zijlstra pointed the 8S machine could have tsc sync issue, and should not be exempted generally arch/x86/kernel/tsc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index cafacb2e58cc..1fa3fdf43159 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1209,7 +1209,7 @@ static void __init check_system_tsc_reliable(void) * - TSC which does not stop in C-States * - the TSC_ADJUST register which allows to detect even minimal * modifications - * - not more than two sockets. As the number of sockets cannot be + * - not more than four sockets. As the number of sockets cannot be * evaluated at the early boot stage where this has to be * invoked, check the number of online memory nodes as a * fallback solution which is an reasonable estimate. @@ -1217,7 +1217,7 @@ static void __init check_system_tsc_reliable(void) if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && boot_cpu_has(X86_FEATURE_NONSTOP_TSC) && boot_cpu_has(X86_FEATURE_TSC_ADJUST) && - nr_online_nodes <= 2) + nr_online_nodes <= 4) tsc_disable_clocksource_watchdog(); }