Commit-ID: fe9af81e524e8a86bdd59c0cc0d9e2b0ccaf840f Gitweb: https://git.kernel.org/tip/fe9af81e524e8a86bdd59c0cc0d9e2b0ccaf840f Author: Pavel Tatashin <pasha.tatas...@oracle.com> AuthorDate: Thu, 19 Jul 2018 16:55:30 -0400 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Fri, 20 Jul 2018 00:02:39 +0200
x86/tsc: Redefine notsc to behave as tsc=unstable Currently, the notsc kernel parameter disables the use of the TSC by sched_clock(). However, this parameter does not prevent the kernel from accessing tsc in other places. The only rationale to boot with notsc is to avoid timing discrepancies on multi-socket systems where TSC are not properly synchronized, and thus exclude TSC from being used for time keeping. But that prevents using TSC as sched_clock() as well, which is not necessary as the core sched_clock() implementation can handle non synchronized TSC based sched clocks just fine. However, there is another method to solve the above problem: booting with tsc=unstable parameter. This parameter allows sched_clock() to use TSC and just excludes it from timekeeping. So there is no real reason to keep notsc, but for compatibility reasons the parameter has to stay. Make it behave like 'tsc=unstable' instead. [ tglx: Massaged changelog ] Signed-off-by: Pavel Tatashin <pasha.tatas...@oracle.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Reviewed-by: Dou Liyang <douly.f...@cn.fujitsu.com> Reviewed-by: Thomas Gleixner <t...@linutronix.de> Cc: steven.sist...@oracle.com Cc: daniel.m.jor...@oracle.com Cc: li...@armlinux.org.uk Cc: schwidef...@de.ibm.com Cc: heiko.carst...@de.ibm.com Cc: john.stu...@linaro.org Cc: sb...@codeaurora.org Cc: h...@zytor.com Cc: pet...@infradead.org Cc: pra...@redhat.com Cc: feng.t...@intel.com Cc: pmla...@suse.com Cc: gno...@lxorguk.ukuu.org.uk Cc: linux-s...@vger.kernel.org Cc: boris.ostrov...@oracle.com Cc: jgr...@suse.com Cc: pbonz...@redhat.com Link: https://lkml.kernel.org/r/20180719205545.16512-12-pasha.tatas...@oracle.com --- Documentation/admin-guide/kernel-parameters.txt | 2 -- Documentation/x86/x86_64/boot-options.txt | 4 +--- arch/x86/kernel/tsc.c | 18 +++--------------- 3 files changed, 4 insertions(+), 20 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 533ff5c68970..5aed30cd0350 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2835,8 +2835,6 @@ nosync [HW,M68K] Disables sync negotiation for all devices. - notsc [BUGS=X86-32] Disable Time Stamp Counter - nowatchdog [KNL] Disable both lockup detectors, i.e. soft-lockup and NMI watchdog (hard-lockup). diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt index 8d109ef67ab6..66114ab4f9fe 100644 --- a/Documentation/x86/x86_64/boot-options.txt +++ b/Documentation/x86/x86_64/boot-options.txt @@ -92,9 +92,7 @@ APICs Timing notsc - Don't use the CPU time stamp counter to read the wall time. - This can be used to work around timing problems on multiprocessor systems - with not properly synchronized CPUs. + Deprecated, use tsc=unstable instead. nohpet Don't use the HPET timer. diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 74392d9d51e0..186395041725 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -38,11 +38,6 @@ EXPORT_SYMBOL(tsc_khz); */ static int __read_mostly tsc_unstable; -/* native_sched_clock() is called before tsc_init(), so - we must start with the TSC soft disabled to prevent - erroneous rdtsc usage on !boot_cpu_has(X86_FEATURE_TSC) processors */ -static int __read_mostly tsc_disabled = -1; - static DEFINE_STATIC_KEY_FALSE(__use_tsc); int tsc_clocksource_reliable; @@ -248,8 +243,7 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable); #ifdef CONFIG_X86_TSC int __init notsc_setup(char *str) { - pr_warn("Kernel compiled with CONFIG_X86_TSC, cannot disable TSC completely\n"); - tsc_disabled = 1; + mark_tsc_unstable("boot parameter notsc"); return 1; } #else @@ -1307,7 +1301,7 @@ unreg: static int __init init_tsc_clocksource(void) { - if (!boot_cpu_has(X86_FEATURE_TSC) || tsc_disabled > 0 || !tsc_khz) + if (!boot_cpu_has(X86_FEATURE_TSC) || !tsc_khz) return 0; if (tsc_unstable) @@ -1414,12 +1408,6 @@ void __init tsc_init(void) set_cyc2ns_scale(tsc_khz, cpu, cyc); } - if (tsc_disabled > 0) - return; - - /* now allow native_sched_clock() to use rdtsc */ - - tsc_disabled = 0; static_branch_enable(&__use_tsc); if (!no_sched_irq_time) @@ -1455,7 +1443,7 @@ unsigned long calibrate_delay_is_known(void) int constant_tsc = cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC); const struct cpumask *mask = topology_core_cpumask(cpu); - if (tsc_disabled || !constant_tsc || !mask) + if (!constant_tsc || !mask) return 0; sibling = cpumask_any_but(mask, cpu);
