Messages in this thread Patch in this message | | | Subject | Re: [PATCH v13 13/18] x86/tsc: calibrate tsc only once | From | Dou Liyang <> | Date | Mon, 16 Jul 2018 17:32:20 +0800 |
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At 07/13/2018 07:30 PM, Pavel Tatashin wrote: > On Fri, Jul 13, 2018 at 3:24 AM Dou Liyang <douly.fnst@cn.fujitsu.com> wrote: >> >> >> At 07/12/2018 08:04 AM, 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(). >>> >>> Suggested-by: Thomas Gleixner <tglx@linutronix.de> >>> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com> >> >> Hi Pavel, >> >> Aha, a complex solution for a simple problem! ;-) And I did find any >> benefits of doing that. did I miss something? > > Hi Dou, > > I had this in previous version: init early, and unconditionally > re-init later (which required to resync sched clocks for continuity, > and check for some other corner cases). Thomas did not like the idea, > as it is less deterministic: it leads for code to work by accident, > where we might get one tsc frequency early and another later, and so > on. The request was to initialize only once, and if that fails do it > again later. This way, if early initialization is broken, we will know > and fix it. >
Hi Pavel,
Yes, right, I have seen the purpose in v12.
>> >> As the cpu_khz and tsc_khz are global variables and the tsc_khz may >> be reset to cpu_khz. How about the following patch. > > Could you please explain where you think this patch can be applied, > and what it fixes? >
This patch is just an simple alternative to realize what you want in your patch. your patch is also good but complex, and need some scrub. eg: - Is it suitable to using the WARN_ON() - the name of determine_cpu_tsc_frequncies() function, s/frequncies/frequencies/. BTW, How about tsc_calibrate_frequencies() - ...
BTW, before this patch, seems we need make sure xen should work well, I can investigate and try to test if we can also move the pagetable_init() to the front of tsc_early_init() for you.
Thanks, dou
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c index da1dbd99cb6e..74cb16d89e25 100644 --- a/arch/x86/kernel/setup.c +++ b/arch/x86/kernel/setup.c @@ -1197,12 +1197,12 @@ void __init setup_arch(char **cmdline_p)
memblock_find_dma_reserve();
+ x86_init.paging.pagetable_init(); + tsc_early_delay_calibrate(); if (!early_xdbc_setup_hardware()) early_xdbc_register_console();
- x86_init.paging.pagetable_init(); - kasan_init();
/* > Thank you, > Pavel > >> >> Thanks, >> dou >> ------------------------8<----------------------------------- >> >> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c >> index 74392d9d51e0..e54fa1037d45 100644 >> --- a/arch/x86/kernel/tsc.c >> +++ b/arch/x86/kernel/tsc.c >> @@ -1370,8 +1370,10 @@ void __init tsc_init(void) >> return; >> } >> >> - cpu_khz = x86_platform.calibrate_cpu(); >> - tsc_khz = x86_platform.calibrate_tsc(); >> + if (!tsc_khz) { >> + cpu_khz = x86_platform.calibrate_cpu(); >> + tsc_khz = x86_platform.calibrate_tsc(); >> + } >> >> /* >> * Trust non-zero tsc_khz as authorative, > > >
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