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block: fix blktrace timestamps

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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: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Ingo Molnar 2008-01-11 13:35:54 +01:00 committed by Jens Axboe
parent a24eab1ed5
commit 2997c8c4a0
1 changed files with 2 additions and 67 deletions
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69
block/blktrace.c
View file

@ -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;
}