The blk_queue_stackable() function was replaced in the 4.14 kernel
by queue_is_rq_based(), commit torvalds/linux@5fdee212. This change
resulted in the default elevator being used which can negatively
impact performance.
Rather than adding additional compatibility code to detect the
new interface unconditionally attempt to set the elevator. Since
we expect this to fail for block devices without an elevator the
error message has been moved in to zfs_dbgmsg().
Finally, it was observed that the elevator_change() was removed
from the 4.12 kernel, commit torvalds/linux@c033269. Update the
comment to clearly specify which are expected to export the
elevator_change() symbol.
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#7645
Certain versions of gcc generate an 'unrecognized command
line option' error message when -Wunused-but-set-variable
is used unconditionally. This in turn can cause several
of the autoconf tests to misdetect an interface.
Now, the use of -Wunused-but-set-variable in the autoconf
tests was introduced by commit b9c59ec8 to address a gcc
4.6 compatibility problem. So we really only need to pass
this option for version of gcc which are known to support it.
Therefore, the tests have been updated to use the result of
the existing ZFS_AC_CONFIG_ALWAYS_NO_UNUSED_BUT_SET_VARIABLE
which determines if gcc supports this option.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1004
As of Linux 2.6.36 an elevator_change() interface was added.
This commit updates vdev_elevator_switch() to use this interface
when available, otherwise it falls back to the usermodehelper
method.
Original-patch-by: foobarz <sysop@xeon.(none)>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#906
