Date:   Tue, 14 Nov 2017 23:50:53 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Mark Salyzyn <salyzyn@...roid.com>, 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

n Tue, 14 Nov 2017, Linus Torvalds wrote:
> On Tue, Nov 14, 2017 at 2:10 PM, Mark Salyzyn <salyzyn@...roid.com> wrote:
> > On 11/14/2017 01:29 PM, Linus Torvalds wrote:
> >>
> >> And then maybe you can send a single patch that changes *ONLY*
> >> print_time(), with an explanation of how Android uses
> >> CONFIG_PRINTK_TIME and would like that to be realtime instead of the
> >> monotonic clock that we traditionally use.
> >
> > print_time() uses msg->ts_nsec; and AFAIK that needs to be in reference to
> > the timebase.
> 
> 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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