fio: fix last block never being touched by random offsets

*Resend with hopefully non mangled patches*
References: <[email protected]>
Content-Disposition: inline; filename=fix_last_block.diff

From: Peter Oberparleiter <[email protected]>

Fix the available range for random offsets which never touched the last block.

Signed-off-by Christian Ehrhardt <[email protected]>

---
[diffstat]

 io_u.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Quoted 17 lines · On Thu, Feb 20 2014, [email protected] wrote:

*Resend with hopefully non mangled patches*
References: <[email protected]>
Content-Disposition: inline; filename=fix_last_block.diff

From: Peter Oberparleiter <[email protected]>

Fix the available range for random offsets which never touched the last block.

Signed-off-by Christian Ehrhardt <[email protected]>

---
[diffstat]

 io_u.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

io_u.c static int __get_next_rand_offset(struct · line 109

Quoted 7 lines

io_u.c +1 -1

@@ -104,7 +104,7 @@ static int __get_next_rand_offset(struct
 
 		dprint(FD_RANDOM, "off rand %llu\n", (unsigned long long) r);
 
-		*b = (lastb - 1) * (r / ((uint64_t) rmax + 1.0));
+		*b = lastb * (r / ((uint64_t) rmax + 1.0));
 	} else {
 		uint64_t off = 0;

Wont this generate lastb as the potentially last block? We want lastb-1 as the last one, otherwise the length of IO from it will be 0.

I might be missing something here.

fio job | grep datafile | sort | uniq

fio job | grep datafile | sort | uniq

Quoted 29 lines · Jens Axboe

Quoted 17 lines · On Thu, Feb 20 2014, [email protected] wrote:

*Resend with hopefully non mangled patches*
References: <[email protected]>
Content-Disposition: inline; filename=fix_last_block.diff

From: Peter Oberparleiter <[email protected]>

Fix the available range for random offsets which never touched the last block.

Signed-off-by Christian Ehrhardt <[email protected]>

---
[diffstat]

  io_u.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

io_u.c static int __get_next_rand_offset(struct · line 109

Quoted 7 lines

io_u.c +1 -1

@@ -104,7 +104,7 @@ static int __get_next_rand_offset(struct
 
  		dprint(FD_RANDOM, "off rand %llu\n", (unsigned long long) r);
 
-		*b = (lastb - 1) * (r / ((uint64_t) rmax + 1.0));
+		*b = lastb * (r / ((uint64_t) rmax + 1.0));
  	} else {
  		uint64_t off = 0;

Wont this generate lastb as the potentially last block? We want lastb-1 as the last one, otherwise the length of IO from it will be 0.

Quoted 1 line

I might be missing something here.

I would expect that the last I/O would be at offset size-blocksize and size blocksize. Consider this example test case that should generate 1 second of random reads with offsets 0 and 512:

[job]
filename=datafile
blocksize=512
size=1024
time_based
runtime=1
rw=randread
norandommap
write_iolog=/dev/stdout

Running it with FIO_VERSION = fio-2.1.5-44-ga1fc produces the following result:

Quoted 1 line

fio job | grep datafile | sort | uniq

datafile add
datafile close
datafile open
datafile read 0 512

-> I/O is only generated for offset 0

Running it with the same version and the subject patch applied:

Quoted 1 line

fio job | grep datafile | sort | uniq

datafile add
datafile close
datafile open
datafile read 0 512
datafile read 512 512

-> Both offsets are covered