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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>,
	steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
	linux@armlinux.org.uk, schwidefsky@de.ibm.com,
	heiko.carstens@de.ibm.com, john.stultz@linaro.org,
	sboyd@codeaurora.org, x86@kernel.org,
	linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com,
	douly.fnst@cn.fujitsu.com, prarit@redhat.com,
	feng.tang@intel.com, pmladek@suse.com,
	gnomes@lxorguk.ukuu.org.uk, linux-s390@vger.kernel.org,
	boris.ostrovsky@oracle.com, jgross@suse.com, pbonzini@redhat.com
Subject: Re: [PATCH v14 20/25] x86/tsc: calibrate tsc only once
Date: Thu, 19 Jul 2018 13:01:22 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1807191300150.1602@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180719103340.GA2494@hirez.programming.kicks-ass.net>

On Thu, 19 Jul 2018, Peter Zijlstra wrote:
> On Tue, Jul 17, 2018 at 10:22:06PM -0400, Pavel Tatashin wrote:
> > During boot tsc is calibrated twice: once in tsc_early_delay_calibrate(),
> > and the second time in tsc_init().
> > 
> > Rename tsc_early_delay_calibrate() to tsc_early_init(), and rework it so
> > the calibration is done only early, and make tsc_init() to use the values
> > already determined in tsc_early_init().
> > 
> > Sometimes it is not possible to determine tsc early, as the subsystem that
> > is required is not yet initialized, in such case try again later in
> > tsc_init().
> 
> It might be nice to preserve some of the information tglx dug out during
> review of all this. Like the various methods of calibrate_*() and their
> dependencies.
> 
> And I note that this patch relies on the magic of native_calibrate_cpu()
> working really early and not exploding in the quick calibration run.
> This either wants fixing or documenting.
> 
> I think the initial idea was to only do the fast_calibrate (cpuid, msr
> and possibly the quick_pit) things early and delay the HPET/PMTIMER
> magic until later.

Yes. I really would prefer to have this as an explicit expressed mechanism
rather than relying on magic variables not being initialized.

Thanks

	tglx


  reply	other threads:[~2018-07-19 11:01 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-18  2:21 [PATCH v14 00/25] Early boot time stamps Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 01/25] x86/kvmclock: Remove memblock dependency Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 02/25] x86/kvmclock: Remove page size requirement from wall_clock Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 03/25] x86/kvmclock: Decrapify kvm_register_clock() Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 04/25] x86/kvmclock: Cleanup the code Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 05/25] x86/kvmclock: Mark variables __initdata and __ro_after_init Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 06/25] x86/kvmclock: Move kvmclock vsyscall param and init to kvmclock Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 07/25] x86/kvmclock: Switch kvmclock data to a PER_CPU variable Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 08/25] x86/kvmclock: Avoid TSC recalibration Pavel Tatashin
2018-07-18 11:14   ` Paolo Bonzini
2018-07-18 13:33     ` Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 09/25] x86: text_poke() may access uninitialized struct pages Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 10/25] x86: initialize static branching early Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 11/25] x86/CPU: Call detect_nopl() only on the BSP Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 12/25] x86/tsc: redefine notsc to behave as tsc=unstable Pavel Tatashin
2018-07-18  2:21 ` [PATCH v14 13/25] x86/xen/time: initialize pv xen time in init_hypervisor_platform Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 14/25] x86/xen/time: output xen sched_clock time from 0 Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 15/25] s390/time: add read_persistent_wall_and_boot_offset() Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 16/25] time: replace read_boot_clock64() with read_persistent_wall_and_boot_offset() Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 17/25] time: default boot time offset to local_clock() Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 18/25] s390/time: remove read_boot_clock64() Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 19/25] ARM/time: " Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 20/25] x86/tsc: calibrate tsc only once Pavel Tatashin
2018-07-19  5:33   ` Dou Liyang
2018-07-19  6:25     ` Thomas Gleixner
2018-07-19  6:48       ` Dou Liyang
2018-07-19 10:33   ` Peter Zijlstra
2018-07-19 11:01     ` Thomas Gleixner [this message]
2018-07-19 15:58       ` Pavel Tatashin
2018-07-19 16:19         ` Thomas Gleixner
2018-07-19 16:49           ` Pavel Tatashin
2018-07-19 18:38             ` Pavel Tatashin
2018-07-19 20:44               ` Thomas Gleixner
2018-07-19 20:46                 ` Pavel Tatashin
2018-07-23  9:28                   ` Alan Cox
2018-07-18  2:22 ` [PATCH v14 21/25] x86/tsc: initialize cyc2ns when tsc freq. is determined Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 22/25] x86/tsc: use tsc early Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 23/25] sched: move sched clock initialization and merge with generic clock Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 24/25] sched: early boot clock Pavel Tatashin
2018-07-19 10:39   ` Peter Zijlstra
2018-07-19 14:16     ` Pavel Tatashin
2018-07-18  2:22 ` [PATCH v14 25/25] sched: use static key for sched_clock_running Pavel Tatashin
2018-07-19 10:48   ` Peter Zijlstra
2018-07-19 14:24     ` Pavel Tatashin

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