Date:   Mon, 29 Jan 2018 12:34:59 -0800
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Prarit Bhargava <prarit@...hat.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT pull] printk updates for 4.15

Any movement on the following proposal? tglx@ do you have an update?

-- Mark

On 11/14/2017 02:50 PM, Thomas Gleixner wrote:
> On Tue, 14 Nov 2017, Linus Torvalds wrote:
>> I'd suggest simply adding another time to the internal 'struct
>> printk_log' (and probably just set it in "log_store()").
>>
>> Doesn't that seem much simpler and more targeted?
>>
>> And exactly because it's targeted and only changes that one thing, now
>> people that don't run Android, and have systemd that actually looks at
>> that timestamp, can _also_ enable that wall clock output if they want
>> to, without it impacting timestamps at all.
>>
>> In fact, I would expect that at that point you actually would want to
>> have multiple different formats that don't necessarily have anything
>> to do with the clock source, but simply with the formatting.
>>
>> Do  you want wallclock to be shown in UTC? Do you want to show it in
>> the system timezeone? Do you want to always show the full resolution,
>> or do you want to show something that takes the previous log entry
>> into account, so it only shows the date if it has actually changed,
>> and maybe shows the time as just a delta if it is small?
>>
>> Because now it's clearly about the freeflowing _text_, not about the
>> timestamp that is processed by tools.
>>
>> The text field done by print_time() really is _that_ different from
>> the timestamp field that is exposed to tools.
>>
>> Yes, somebody might still be parsing it, and maybe then you need to
>> set that text field to a legacy format anyway, but at least it's a
>> whole lot easier to explain what's going on.
> Something like the untested patch below should do the storage and converts
> the primary timestamp from local_clock() to clock monotonic.
>
> The print out and /dev/kmsg is unchanged. That's a separate story.
>
> Thanks,
>
> 	tglx
>
> 8<-------------------
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -352,7 +352,11 @@ enum log_flags {
>   };
>   
>   struct printk_log {
> -	u64 ts_nsec;		/* timestamp in nanoseconds */
> +	/* Timestamps in nanoseconds */
> +	union {
> +		u64			ts_nsec;
> +		struct timestamps	ts;
> +	};
>   	u16 len;		/* length of entire record */
>   	u16 text_len;		/* length of text buffer */
>   	u16 dict_len;		/* length of dictionary buffer */
> @@ -578,7 +582,7 @@ static u32 truncate_msg(u16 *text_len, u
>   
>   /* insert record into the buffer, discard old ones, update heads */
>   static int log_store(int facility, int level,
> -		     enum log_flags flags, u64 ts_nsec,
> +		     enum log_flags flags, struct timestamps *ts,
>   		     const char *dict, u16 dict_len,
>   		     const char *text, u16 text_len)
>   {
> @@ -621,10 +625,10 @@ static int log_store(int facility, int l
>   	msg->facility = facility;
>   	msg->level = level & 7;
>   	msg->flags = flags & 0x1f;
> -	if (ts_nsec > 0)
> -		msg->ts_nsec = ts_nsec;
> +	if (ts && ts->mono  > 0)
> +		msg->ts = *ts;
>   	else
> -		msg->ts_nsec = local_clock();
> +		ktime_get_fast_timestamps(&msg->ts);
>   	memset(log_dict(msg) + dict_len, 0, pad_len);
>   	msg->len = size;
>   
> @@ -687,7 +691,7 @@ static void append_char(char **pp, char
>   static ssize_t msg_print_ext_header(char *buf, size_t size,
>   				    struct printk_log *msg, u64 seq)
>   {
> -	u64 ts_usec = msg->ts_nsec;
> +	u64 ts_usec = msg->ts.mono;
>   
>   	do_div(ts_usec, 1000);
>   
> @@ -1022,6 +1026,7 @@ void log_buf_vmcoreinfo_setup(void)
>   	 */
>   	VMCOREINFO_STRUCT_SIZE(printk_log);
>   	VMCOREINFO_OFFSET(printk_log, ts_nsec);
> +	VMCOREINFO_OFFSET(printk_log, ts);
>   	VMCOREINFO_OFFSET(printk_log, len);
>   	VMCOREINFO_OFFSET(printk_log, text_len);
>   	VMCOREINFO_OFFSET(printk_log, dict_len);
> @@ -1204,17 +1209,18 @@ static inline void boot_delay_msec(int l
>   static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
>   module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
>   
> -static size_t print_time(u64 ts, char *buf)
> +static size_t print_time(const struct timestamps *ts, char *buf)
>   {
>   	unsigned long rem_nsec;
> +	u64 mono = ts->mono;
>   
>   	if (!printk_time)
>   		return 0;
>   
> -	rem_nsec = do_div(ts, 1000000000);
> +	rem_nsec = do_div(mono, 1000000000);
>   
>   	if (!buf)
> -		return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
> +		return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)mono);
>   
>   	return sprintf(buf, "[%5lu.%06lu] ",
>   		       (unsigned long)ts, rem_nsec / 1000);
> @@ -1239,7 +1245,7 @@ static size_t print_prefix(const struct
>   		}
>   	}
>   
> -	len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
> +	len += print_time(&msg->ts, buf ? buf + len : NULL);
>   	return len;
>   }
>   
> @@ -1599,7 +1605,7 @@ static struct cont {
>   	char buf[LOG_LINE_MAX];
>   	size_t len;			/* length == 0 means unused buffer */
>   	struct task_struct *owner;	/* task of first print*/
> -	u64 ts_nsec;			/* time of first print */
> +	struct timestamps ts;		/* time of first print */
>   	u8 level;			/* log level of first message */
>   	u8 facility;			/* log facility of first message */
>   	enum log_flags flags;		/* prefix, newline flags */
> @@ -1610,7 +1616,7 @@ static void cont_flush(void)
>   	if (cont.len == 0)
>   		return;
>   
> -	log_store(cont.facility, cont.level, cont.flags, cont.ts_nsec,
> +	log_store(cont.facility, cont.level, cont.flags, &cont.ts,
>   		  NULL, 0, cont.buf, cont.len);
>   	cont.len = 0;
>   }
> @@ -1631,7 +1637,7 @@ static bool cont_add(int facility, int l
>   		cont.facility = facility;
>   		cont.level = level;
>   		cont.owner = current;
> -		cont.ts_nsec = local_clock();
> +		ktime_get_fast_timestamps(&cont.ts);
>   		cont.flags = flags;
>   	}
>   
> @@ -1677,7 +1683,8 @@ static size_t log_output(int facility, i
>   	}
>   
>   	/* Store it in the record log */
> -	return log_store(facility, level, lflags, 0, dict, dictlen, text, text_len);
> +	return log_store(facility, level, lflags, NULL, dict, dictlen, text,
> +			 text_len);
>   }
>   
>   asmlinkage int vprintk_emit(int facility, int level,
> --- a/include/linux/timekeeping.h
> +++ b/include/linux/timekeeping.h
> @@ -146,7 +146,19 @@ extern void timekeeping_inject_sleeptime
>    * PPS accessor
>    */
>   extern void ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw,
> -				        struct timespec64 *ts_real);
> +					struct timespec64 *ts_real);
> +
> +/*
> + * struct timestanps - Simultaneous mono/boot/real timestamps
> + * @mono:	Monotonic timestamp
> + * @boot:	Boottime timestamp
> + * @real:	Realtime timestamp
> + */
> +struct timestamps {
> +	u64		mono;
> +	u64		boot;
> +	u64		real;
> +};
>   
>   /*
>    * struct system_time_snapshot - simultaneous raw/real time capture with
> @@ -206,6 +218,9 @@ extern int get_device_system_crosststamp
>    */
>   extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
>   
> +/* NMI safe mono/boot/realtime timestamps */
> +extern void ktime_get_fast_timestamps(struct timestamps *snap);
> +
>   /*
>    * Persistent clock related interfaces
>    */
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -496,29 +496,29 @@ u64 notrace ktime_get_boot_fast_ns(void)
>   }
>   EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);
>   
> -
>   /*
>    * See comment for __ktime_get_fast_ns() vs. timestamp ordering
>    */
> -static __always_inline u64 __ktime_get_real_fast_ns(struct tk_fast *tkf)
> +static notrace u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
>   {
>   	struct tk_read_base *tkr;
> +	u64 basem, baser, delta;
>   	unsigned int seq;
> -	u64 now;
>   
>   	do {
>   		seq = raw_read_seqcount_latch(&tkf->seq);
>   		tkr = tkf->base + (seq & 0x01);
> -		now = ktime_to_ns(tkr->base_real);
> +		basem = ktime_to_ns(tkr->base);
> +		baser = ktime_to_ns(tkr->base_real);
>   
> -		now += timekeeping_delta_to_ns(tkr,
> -				clocksource_delta(
> -					tk_clock_read(tkr),
> -					tkr->cycle_last,
> -					tkr->mask));
> +		delta = timekeeping_delta_to_ns(tkr,
> +				clocksource_delta(tk_clock_read(tkr),
> +				tkr->cycle_last, tkr->mask));
>   	} while (read_seqcount_retry(&tkf->seq, seq));
>   
> -	return now;
> +	if (mono)
> +		*mono = basem + delta;
> +	return baser + delta;
>   }
>   
>   /**
> @@ -526,11 +526,25 @@ static __always_inline u64 __ktime_get_r
>    */
>   u64 ktime_get_real_fast_ns(void)
>   {
> -	return __ktime_get_real_fast_ns(&tk_fast_mono);
> +	return __ktime_get_real_fast(&tk_fast_mono, NULL);
>   }
>   EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
>   
>   /**
> + * ktime_get_fast_timestamps: - NMI safe timestamps
> + * @snap:	Pointer to timestamp storage
> + *
> + * Stores clock monotonic, boottime and realtime time stamps
> + */
> +void ktime_get_fast_timestamps(struct timestamps *snap)
> +{
> +	struct timekeeper *tk = &tk_core.timekeeper;
> +
> +	snap->real = __ktime_get_real_fast(&tk_fast_mono, &snap->mono);
> +	snap->boot = snap->mono + ktime_to_ns(tk->offs_boot);
> +}
> +
> +/**
>    * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
>    * @tk: Timekeeper to snapshot.
>    *

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