linux-kernel - Re: [tip:x86/debug] x86/timers: Add simple udelay calibration

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Message-ID: <59262A15.4080402@linux.intel.com>
Date:   Thu, 25 May 2017 08:49:25 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>, brgerst@...il.com,
        mathias.nyman@...ux.intel.com, dvlasenk@...hat.com,
        tglx@...utronix.de, peterz@...radead.org, bp@...en8.de,
        luto@...nel.org, torvalds@...ux-foundation.org, hpa@...or.com,
        jpoimboe@...hat.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/debug] x86/timers: Add simple udelay calibration

Hi,

On 05/25/2017 12:56 AM, Jan Kiszka wrote:
> On 2017-03-21 13:19, tip-bot for Lu Baolu wrote:
>> Commit-ID:  dd759d93f4dd4fd2f345a78ad1223bb3edf3ee7b
>> Gitweb:     http://git.kernel.org/tip/dd759d93f4dd4fd2f345a78ad1223bb3edf3ee7b
>> Author:     Lu Baolu <baolu.lu@...ux.intel.com>
>> AuthorDate: Tue, 21 Mar 2017 16:01:29 +0800
>> Committer:  Ingo Molnar <mingo@...nel.org>
>> CommitDate: Tue, 21 Mar 2017 12:28:45 +0100
>>
>> x86/timers: Add simple udelay calibration
>>
>> Add a simple udelay calibration in x86 architecture-specific
>> boot-time initializations. This will get a workable estimate
>> for loops_per_jiffy. Hence, udelay() could be used after this
>> initialization.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> Acked-by: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: Brian Gerst <brgerst@...il.com>
>> Cc: Denys Vlasenko <dvlasenk@...hat.com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: H. Peter Anvin <hpa@...or.com>
>> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Mathias Nyman <mathias.nyman@...ux.intel.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: linux-usb@...r.kernel.org
>> Link: http://lkml.kernel.org/r/1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com
>> Signed-off-by: Ingo Molnar <mingo@...nel.org>
>> ---
>>  arch/x86/kernel/setup.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>> index 4bf0c89..e70204e 100644
>> --- a/arch/x86/kernel/setup.c
>> +++ b/arch/x86/kernel/setup.c
>> @@ -837,6 +837,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>>  	return 0;
>>  }
>>  
>> +static void __init simple_udelay_calibration(void)
>> +{
>> +	unsigned int tsc_khz, cpu_khz;
>> +	unsigned long lpj;
>> +
>> +	if (!boot_cpu_has(X86_FEATURE_TSC))
>> +		return;
>> +
>> +	cpu_khz = x86_platform.calibrate_cpu();
>> +	tsc_khz = x86_platform.calibrate_tsc();
>> +
>> +	tsc_khz = tsc_khz ? : cpu_khz;
>> +	if (!tsc_khz)
>> +		return;
>> +
>> +	lpj = tsc_khz * 1000;
>> +	do_div(lpj, HZ);
>> +	loops_per_jiffy = lpj;
>> +}
>> +
>>  /*
>>   * Determine if we were loaded by an EFI loader.  If so, then we have also been
>>   * passed the efi memmap, systab, etc., so we should use these data structures
>> @@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p)
>>  	 */
>>  	x86_configure_nx();
>>  
>> +	simple_udelay_calibration();
>> +
>>  	parse_early_param();
>>  
>>  #ifdef CONFIG_MEMORY_HOTPLUG
>>
> Can we move this past init_hypervisor_platform()?

Yes, we can as far as I can see.

Best regards,
Lu Baolu

>  Otherwise, the
> x86_platform hooks aren't fully initialized yet, and we may use the
> wrong functions.
>
> Jan
>