Commit 2997c8c4 authored by Ingo Molnar's avatar Ingo Molnar Committed by Jens Axboe
Browse files

block: fix blktrace timestamps 



David Dillow reported broken blktrace timestamps. The reason
is cpu_clock() which is not a global time source.

Fix bkltrace timestamps by using ktime_get() like the networking
code does for packet timestamps. This also removes a whole lot
of complexity from bkltrace.c and shrinks the code by 500 bytes:

   text    data     bss     dec     hex filename
   2888     124      44    3056     bf0 blktrace.o.before
   2390     116      44    2550     9f6 blktrace.o.after

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent a24eab1e

block/blktrace.c

+2 −67
Original line number Diff line number Diff line
@@ -25,7 +25,6 @@ 
#include <linux/time.h>

#include <asm/uaccess.h>



static DEFINE_PER_CPU(unsigned long long, blk_trace_cpu_offset) = { 0, };

static unsigned int blktrace_seq __read_mostly = 1;



/*
@@ -41,7 +40,7 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action, 
		const int cpu = smp_processor_id();



		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;

		t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);

		t->time = ktime_to_ns(ktime_get());

		t->device = bt->dev;

		t->action = action;

		t->pid = pid;
@@ -159,7 +158,7 @@ void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes, 


		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;

		t->sequence = ++(*sequence);

		t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu);

		t->time = ktime_to_ns(ktime_get());

		t->sector = sector;

		t->bytes = bytes;

		t->action = what;
@@ -506,73 +505,9 @@ void blk_trace_shutdown(struct request_queue *q) 
	}

}



/*

 * Average offset over two calls to cpu_clock() with a gettimeofday()

 * in the middle

 */

static void blk_check_time(unsigned long long *t, int this_cpu)

{

	unsigned long long a, b;

	struct timeval tv;



	a = cpu_clock(this_cpu);

	do_gettimeofday(&tv);

	b = cpu_clock(this_cpu);



	*t = tv.tv_sec * 1000000000 + tv.tv_usec * 1000;

	*t -= (a + b) / 2;

}



/*

 * calibrate our inter-CPU timings

 */

static void blk_trace_check_cpu_time(void *data)

{

	unsigned long long *t;

	int this_cpu = get_cpu();



	t = &per_cpu(blk_trace_cpu_offset, this_cpu);



	/*

	 * Just call it twice, hopefully the second call will be cache hot

	 * and a little more precise

	 */

	blk_check_time(t, this_cpu);

	blk_check_time(t, this_cpu);



	put_cpu();

}



static void blk_trace_set_ht_offsets(void)

{

#if defined(CONFIG_SCHED_SMT)

	int cpu, i;



	/*

	 * now make sure HT siblings have the same time offset

	 */

	preempt_disable();

	for_each_online_cpu(cpu) {

		unsigned long long *cpu_off, *sibling_off;



		for_each_cpu_mask(i, per_cpu(cpu_sibling_map, cpu)) {

			if (i == cpu)

				continue;



			cpu_off = &per_cpu(blk_trace_cpu_offset, cpu);

			sibling_off = &per_cpu(blk_trace_cpu_offset, i);

			*sibling_off = *cpu_off;

		}

	}

	preempt_enable();

#endif

}



static __init int blk_trace_init(void)

{

	mutex_init(&blk_tree_mutex);

	on_each_cpu(blk_trace_check_cpu_time, NULL, 1, 1);

	blk_trace_set_ht_offsets();



	return 0;

}

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