linux-kernel - Re: [patch V2 44/64] x86: kvm: Make kvm_get_time_and

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Date:	Thu, 17 Jul 2014 12:58:57 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
CC:	John Stultz <john.stultz@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Gleb Natapov <gleb@...nel.org>, kvm@...r.kernel.org
Subject: Re: [patch V2 44/64] x86: kvm: Make kvm_get_time_and_clockread()
 nanoseconds based

Il 16/07/2014 23:04, Thomas Gleixner ha scritto:
> Convert the relevant base data right away to nanoseconds instead of
> doing the conversion on every readout. Reduces text size by 160 bytes.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Gleb Natapov <gleb@...nel.org>
> Cc: kvm@...r.kernel.org
> ---
>  arch/x86/kvm/x86.c |   44 ++++++++++++++------------------------------
>  1 file changed, 14 insertions(+), 30 deletions(-)
>
> Index: tip/arch/x86/kvm/x86.c
> ===================================================================
> --- tip.orig/arch/x86/kvm/x86.c
> +++ tip/arch/x86/kvm/x86.c
> @@ -984,9 +984,8 @@ struct pvclock_gtod_data {
>  		u32	shift;
>  	} clock;
>
> -	/* open coded 'struct timespec' */
> -	u64		monotonic_time_snsec;
> -	time_t		monotonic_time_sec;
> +	u64		boot_ns;
> +	u64		nsec_base;
>  };
>
>  static struct pvclock_gtod_data pvclock_gtod_data;
> @@ -994,6 +993,9 @@ static struct pvclock_gtod_data pvclock_
>  static void update_pvclock_gtod(struct timekeeper *tk)
>  {
>  	struct pvclock_gtod_data *vdata = &pvclock_gtod_data;
> +	u64 boot_ns;
> +
> +	boot_ns = ktime_to_ns(ktime_add(tk->base_mono, tk->offs_boot));
>
>  	write_seqcount_begin(&vdata->seq);
>
> @@ -1004,17 +1006,8 @@ static void update_pvclock_gtod(struct t
>  	vdata->clock.mult		= tk->mult;
>  	vdata->clock.shift		= tk->shift;
>
> -	vdata->monotonic_time_sec	= tk->xtime_sec
> -					+ tk->wall_to_monotonic.tv_sec;
> -	vdata->monotonic_time_snsec	= tk->xtime_nsec
> -					+ (tk->wall_to_monotonic.tv_nsec
> -						<< tk->shift);
> -	while (vdata->monotonic_time_snsec >=
> -					(((u64)NSEC_PER_SEC) << tk->shift)) {
> -		vdata->monotonic_time_snsec -=
> -					((u64)NSEC_PER_SEC) << tk->shift;
> -		vdata->monotonic_time_sec++;
> -	}
> +	vdata->boot_ns			= boot_ns;
> +	vdata->nsec_base		= tk->xtime_nsec;
>
>  	write_seqcount_end(&vdata->seq);
>  }
> @@ -1371,23 +1364,22 @@ static inline u64 vgettsc(cycle_t *cycle
>  	return v * gtod->clock.mult;
>  }
>
> -static int do_monotonic(struct timespec *ts, cycle_t *cycle_now)
> +static int do_monotonic_boot(s64 *t, cycle_t *cycle_now)
>  {
> +	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
>  	unsigned long seq;
> -	u64 ns;
>  	int mode;
> -	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
> +	u64 ns;
>
> -	ts->tv_nsec = 0;
>  	do {
>  		seq = read_seqcount_begin(&gtod->seq);
>  		mode = gtod->clock.vclock_mode;
> -		ts->tv_sec = gtod->monotonic_time_sec;
> -		ns = gtod->monotonic_time_snsec;
> +		ns = gtod->nsec_base;
>  		ns += vgettsc(cycle_now);
>  		ns >>= gtod->clock.shift;
> +		ns += gtod->boot_ns;
>  	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
> -	timespec_add_ns(ts, ns);
> +	*t = ns;
>
>  	return mode;
>  }
> @@ -1395,19 +1387,11 @@ static int do_monotonic(struct timespec
>  /* returns true if host is using tsc clocksource */
>  static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
>  {
> -	struct timespec ts;
> -
>  	/* checked again under seqlock below */
>  	if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
>  		return false;
>
> -	if (do_monotonic(&ts, cycle_now) != VCLOCK_TSC)
> -		return false;
> -
> -	monotonic_to_bootbased(&ts);
> -	*kernel_ns = timespec_to_ns(&ts);
> -
> -	return true;
> +	return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
>  }
>  #endif
>
>
>

Acked-by: Paolo Bonzini <pbonzini@...hat.com>
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