linux-kernel - Re: [RFC PATCH 4/4] treewide: Use clocksource id for struct system_counterval

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Message-ID: <2d86145b-4b70-5f3b-cf54-a6994ce24783@opensynergy.com>
Date:   Fri, 15 Sep 2023 16:29:26 +0200
From:   Peter Hilber <peter.hilber@...nsynergy.com>
To:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.linux.dev
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Richard Cochran <richardcochran@...il.com>,
        John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>, netdev@...r.kernel.org,
        Marc Zyngier <maz@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH 4/4] treewide: Use clocksource id for struct
 system_counterval_t

On 15.09.23 15:30, Thomas Gleixner wrote:
> Peter!
> 
> On Fri, Aug 18 2023 at 03:12, Peter Hilber wrote:
>> --- a/arch/x86/kernel/tsc.c
>> +++ b/arch/x86/kernel/tsc.c
>> @@ -1313,7 +1313,7 @@ struct system_counterval_t convert_art_to_tsc(u64 art)
>>  	res += tmp + art_to_tsc_offset;
>>  
>>  	return (struct system_counterval_t) {
>> -		.cs = have_art ? &clocksource_tsc : NULL,
>> +		.cs_id = have_art ? CSID_TSC : CSID_GENERIC,
>>  		.cycles = res
> 
> Can you please change all of this so that:
> 
>     patch 1:   Adds cs_id to struct system_counterval_t
>     patch 2-4: Add the clocksource ID and set the cs_id field
>     patch 5:   Switches the core to evaluate cs_id
>     patch 6:   Remove the cs field from system_counterval_t

OK. For 2-4, I assume split x86/tsc, x86/kvm, drivers/ptp (which
also handles the CSID_ARM_ARCH_COUNTER case).

>> --- a/include/linux/timekeeping.h
>> +++ b/include/linux/timekeeping.h
>> @@ -270,12 +270,12 @@ struct system_device_crosststamp {
>>   * struct system_counterval_t - system counter value with the pointer to the
>>   *				corresponding clocksource
>>   * @cycles:	System counter value
>> - * @cs:		Clocksource corresponding to system counter value. Used by
>> + * @cs_id:	Clocksource corresponding to system counter value. Used by
>>   *		timekeeping code to verify comparibility of two cycle values
> 
> That comment is inaccurate. It's not longer the clocksource itself. It's
> the ID which is used for validation.

I will change the comment to refer to "Clocksource ID".

Thanks for the advice!

Peter