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The following changes since commit 23f394d5d70902c6f1d71ac03fa1d70e13c9c0b9:

  Scramble on a 512b boundary (2011-09-16 22:47:15 +0200)

are available in the git repository at:
  git://git.kernel.dk/fio.git master

Jens Axboe (2):
      Add option for controlling buffer scrambling
      Scramble fix

 HOWTO     |    7 +++++++
 fio.1     |    7 +++++++
 fio.h     |    1 +
 io_u.c    |   23 ++++++++++++++---------
 options.c |    7 +++++++
 5 files changed, 36 insertions(+), 9 deletions(-)

---

Diff of recent changes:

diff --git a/HOWTO b/HOWTO
index b67a201..cc2df9b 100644
--- a/HOWTO
+++ b/HOWTO
@@ -481,6 +481,13 @@ refill_buffers	If this option is given, fio will refill the IO buffers
 		isn't specified, naturally. If data verification is enabled,
 		refill_buffers is also automatically enabled.
 
+scramble_buffers=bool	If refill_buffers is too costly and the target is
+		using data deduplication, then setting this option will
+		slightly modify the IO buffer contents to defeat normal
+		de-dupe attempts. This is not enough to defeat more clever
+		block compression attempts, but it will stop naive dedupe of
+		blocks. Default: true.
+
 nrfiles=int	Number of files to use for this job. Defaults to 1.
 
 openfiles=int	Number of files to keep open at the same time. Defaults to
diff --git a/fio.1 b/fio.1
index e8fb57f..dc10b40 100644
--- a/fio.1
+++ b/fio.1
@@ -329,6 +329,13 @@ default is to only fill it at init time and reuse that data. Only makes sense
 if zero_buffers isn't specified, naturally. If data verification is enabled,
 refill_buffers is also automatically enabled.
 .TP
+.BI scramble_buffers \fR=\fPbool
+If \fBrefill_buffers\fR is too costly and the target is using data
+deduplication, then setting this option will slightly modify the IO buffer
+contents to defeat normal de-dupe attempts. This is not enough to defeat
+more clever block compression attempts, but it will stop naive dedupe
+of blocks. Default: true.
+.TP
 .BI nrfiles \fR=\fPint
 Number of files to use for this job.  Default: 1.
 .TP
diff --git a/fio.h b/fio.h
index e93e8f3..022ba57 100644
--- a/fio.h
+++ b/fio.h
@@ -348,6 +348,7 @@ struct thread_options {
 	enum fio_fallocate_mode fallocate_mode;
 	unsigned int zero_buffers;
 	unsigned int refill_buffers;
+	unsigned int scramble_buffers;
 	unsigned int time_based;
 	unsigned int disable_lat;
 	unsigned int disable_clat;
diff --git a/io_u.c b/io_u.c
index f4c4aa2..38efcc1 100644
--- a/io_u.c
+++ b/io_u.c
@@ -1129,6 +1129,7 @@ static int check_get_verify(struct thread_data *td, struct io_u *io_u)
 static void small_content_scramble(struct io_u *io_u)
 {
 	unsigned int i, nr_blocks = io_u->buflen / 512;
+	unsigned long long boffset;
 	unsigned int offset;
 	void *p, *end;
 
@@ -1136,20 +1137,23 @@ static void small_content_scramble(struct io_u *io_u)
 		return;
 
 	p = io_u->xfer_buf;
+	boffset= io_u->offset;
+
 	for (i = 0; i < nr_blocks; i++) {
 		/*
 		 * Fill the byte offset into a "random" start offset of
 		 * the buffer, given by the product of the usec time
 		 * and the actual offset.
 		 */
-		offset = (io_u->start_time.tv_usec * io_u->offset) & 511;
+		offset = (io_u->start_time.tv_usec ^ boffset) & 511;
 		if (offset >= 512 - sizeof(unsigned long long))
 			offset -= sizeof(unsigned long long);
-		*((unsigned long long *) p + offset) = io_u->offset;
+		*((unsigned long long *) p + offset) = boffset;
 
 		end = p + 512 - sizeof(io_u->start_time);
 		memcpy(end, &io_u->start_time, sizeof(io_u->start_time));
 		p += 512;
+		boffset += 512;
 	}
 }
 
@@ -1203,13 +1207,14 @@ struct io_u *get_io_u(struct thread_data *td)
 		f->last_start = io_u->offset;
 		f->last_pos = io_u->offset + io_u->buflen;
 
-		if (td->o.verify != VERIFY_NONE && io_u->ddir == DDIR_WRITE)
-			populate_verify_io_u(td, io_u);
-		else if (td->o.refill_buffers && io_u->ddir == DDIR_WRITE)
-			io_u_fill_buffer(td, io_u, io_u->xfer_buflen);
-		else if (io_u->ddir == DDIR_WRITE)
-			do_scramble = 1;
-		else if (io_u->ddir == DDIR_READ) {
+		if (io_u->ddir == DDIR_WRITE) {
+			if (td->o.verify != VERIFY_NONE)
+				populate_verify_io_u(td, io_u);
+			else if (td->o.refill_buffers)
+				io_u_fill_buffer(td, io_u, io_u->xfer_buflen);
+			else if (td->o.scramble_buffers)
+				do_scramble = 1;
+		} else if (io_u->ddir == DDIR_READ) {
 			/*
 			 * Reset the buf_filled parameters so next time if the
 			 * buffer is used for writes it is refilled.
diff --git a/options.c b/options.c
index 74c24d0..5252477 100644
--- a/options.c
+++ b/options.c
@@ -1967,6 +1967,13 @@ static struct fio_option options[FIO_MAX_OPTS] = {
 		.help	= "Refill IO buffers on every IO submit",
 	},
 	{
+		.name	= "scramble_buffers",
+		.type	= FIO_OPT_BOOL,
+		.off1	= td_var_offset(scramble_buffers),
+		.help	= "Slightly scramble buffers on every IO submit",
+		.def	= "1",
+	},
+	{
 		.name	= "clat_percentiles",
 		.type	= FIO_OPT_BOOL,
 		.off1	= td_var_offset(clat_percentiles),
--
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