On 11/21/22 13:29, Alberto Faria wrote:
When set, the queue's completion fd is enabled even when it isn't used,
i.e., even if option libblkio_wait_mode is _not_ set to "eventfd".
Depending on the libblkio driver, this can have an impact on
performance. This option allows evaluating that overhead.
Signed-off-by: Alberto Faria <afaria@xxxxxxxxxx>
---
HOWTO.rst | 9 ++++++++-
engines/libblkio.c | 21 +++++++++++++++++++--
fio.1 | 10 +++++++++-
3 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/HOWTO.rst b/HOWTO.rst
index 4b059cb2..7b3a3ffc 100644
--- a/HOWTO.rst
+++ b/HOWTO.rst
@@ -2333,7 +2333,8 @@ with the caveat that when used on the command line, they must come after the
[libblkio]
Use poll queues. This is incompatible with
- :option:`libblkio_wait_mode=eventfd <libblkio_wait_mode>`.
+ :option:`libblkio_wait_mode=eventfd <libblkio_wait_mode>` and
+ :option:`libblkio_force_enable_completion_eventfd`.
[pvsync2]
@@ -2896,6 +2897,12 @@ with the caveat that when used on the command line, they must come after the
**loop**
Use a busy loop with a non-blocking call to ``blkioq_do_io()``.
+.. option:: libblkio_force_enable_completion_eventfd=bool : [libblkio]
Same comment as for previous patches regarding option types.
+
+ Enable the ``struct blkioq``'s completion eventfd even when unused. This
+ may impact performance. The default is to enable it only if
+ :option:`libblkio_wait_mode` is **eventfd**.
+
I/O depth
~~~~~~~~~
diff --git a/engines/libblkio.c b/engines/libblkio.c
index d7666f69..3ff87e6d 100644
--- a/engines/libblkio.c
+++ b/engines/libblkio.c
@@ -37,6 +37,7 @@ struct fio_blkio_options {
unsigned int vectored;
unsigned int write_zeroes_on_trim;
enum fio_blkio_wait_mode wait_mode;
+ unsigned int force_enable_completion_eventfd;
};
static struct fio_option options[] = {
@@ -120,6 +121,16 @@ static struct fio_option options[] = {
.category = FIO_OPT_C_ENGINE,
.group = FIO_OPT_G_LIBBLKIO,
},
+ {
+ .name = "libblkio_force_enable_completion_eventfd",
+ .lname = "Force enable the completion eventfd, even if unused",
+ .type = FIO_OPT_STR_SET,
+ .off1 = offsetof(struct fio_blkio_options,
+ force_enable_completion_eventfd),
+ .help = "This can impact performance",
+ .category = FIO_OPT_C_ENGINE,
+ .group = FIO_OPT_G_LIBBLKIO,
+ },
{
.name = NULL,
@@ -283,6 +294,11 @@ static int fio_blkio_setup(struct thread_data *td)
return 1;
}
+ if (options->hipri && options->force_enable_completion_eventfd) {
+ log_err("fio: option hipri is incompatible with option libblkio_force_enable_completion_eventfd\n");
+ return 1;
+ }
+
/* get target size */
if (fio_blkio_create_and_connect(td, &b) != 0)
@@ -308,7 +324,7 @@ out_blkio_destroy:
struct fio_blkio_data {
struct blkio *b;
struct blkioq *q;
- int completion_fd; /* -1 if not FIO_BLKIO_WAIT_MODE_EVENTFD */
+ int completion_fd; /* may be -1 if not FIO_BLKIO_WAIT_MODE_EVENTFD */
bool has_mem_region; /* whether mem_region is valid */
struct blkio_mem_region mem_region; /* only if allocated by libblkio */
@@ -368,7 +384,8 @@ static int fio_blkio_init(struct thread_data *td)
/* enable completion fd and make it blocking */
- if (options->wait_mode == FIO_BLKIO_WAIT_MODE_EVENTFD) {
+ if (options->wait_mode == FIO_BLKIO_WAIT_MODE_EVENTFD ||
+ options->force_enable_completion_eventfd) {
blkioq_set_completion_fd_enabled(data->q, true);
data->completion_fd = blkioq_get_completion_fd(data->q);
diff --git a/fio.1 b/fio.1
index 88bb232f..e2f92bd1 100644
--- a/fio.1
+++ b/fio.1
@@ -2622,7 +2622,8 @@ before starting the \fBstruct blkio\fR. Each property must have the format
the engine sets any other properties, so those can be overriden.
.TP
.BI (libblkio)hipri \fR=\fPbool
-Use poll queues. This is incompatible with \fBlibblkio_wait_mode=eventfd\fR.
+Use poll queues. This is incompatible with \fBlibblkio_wait_mode=eventfd\fR and
+\fBlibblkio_force_enable_completion_eventfd\fR.
.TP
.BI (libblkio)libblkio_vectored \fR=\fPbool
Submit vectored read and write requests. Default is 0.
@@ -2644,6 +2645,13 @@ Use a blocking call to \fBread()\fR on the completion eventfd.
.TP
.B loop
Use a busy loop with a non-blocking call to \fBblkioq_do_io()\fR.
+.RE
+.RE
+.TP
+.BI (libblkio)libblkio_force_enable_completion_eventfd \fR=\fPbool
+Enable the \fBstruct blkioq\fR's completion eventfd even when unused. This may
+impact performance. The default is to enable it only if \fBlibblkio_wait_mode\fR
+is \fBeventfd\fR.
.SS "I/O depth"
.TP
.BI iodepth \fR=\fPint
