From b5ee3df7765cd3b46c28f2b1ff3f8d9895f4155c Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Tue, 19 Jun 2018 21:52:45 -0700 Subject: [PATCH] Linux 4.14 compat: blk_queue_stackable() 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 Reviewed-by: Tony Hutter Signed-off-by: Brian Behlendorf Closes #7645 --- config/kernel-elevator-change.m4 | 4 ++-- include/linux/blkdev_compat.h | 11 ----------- module/zfs/vdev_disk.c | 22 ++++++++++------------ 3 files changed, 12 insertions(+), 25 deletions(-) diff --git a/config/kernel-elevator-change.m4 b/config/kernel-elevator-change.m4 index ace5aa82d3..eba252579b 100644 --- a/config/kernel-elevator-change.m4 +++ b/config/kernel-elevator-change.m4 @@ -1,6 +1,6 @@ dnl # -dnl # 2.6.36 API change -dnl # Verify the elevator_change() symbol is available. +dnl # 2.6.36 API, exported elevator_change() symbol +dnl # 4.12 API, removed elevator_change() symbol dnl # AC_DEFUN([ZFS_AC_KERNEL_ELEVATOR_CHANGE], [ AC_MSG_CHECKING([whether elevator_change() is available]) diff --git a/include/linux/blkdev_compat.h b/include/linux/blkdev_compat.h index 27f0566266..c8cdf38ef4 100644 --- a/include/linux/blkdev_compat.h +++ b/include/linux/blkdev_compat.h @@ -105,17 +105,6 @@ blk_queue_set_write_cache(struct request_queue *q, bool wc, bool fua) #define blk_fs_request(rq) ((rq)->cmd_type == REQ_TYPE_FS) #endif -/* - * 2.6.27 API change, - * The blk_queue_stackable() queue flag was added in 2.6.27 to handle dm - * stacking drivers. Prior to this request stacking drivers were detected - * by checking (q->request_fn == NULL), for earlier kernels we revert to - * this legacy behavior. - */ -#ifndef blk_queue_stackable -#define blk_queue_stackable(q) ((q)->request_fn == NULL) -#endif - /* * 2.6.34 API change, * The blk_queue_max_hw_sectors() function replaces blk_queue_max_sectors(). diff --git a/module/zfs/vdev_disk.c b/module/zfs/vdev_disk.c index 6dc0544fc6..c5708cb2b5 100644 --- a/module/zfs/vdev_disk.c +++ b/module/zfs/vdev_disk.c @@ -168,23 +168,20 @@ vdev_elevator_switch(vdev_t *v, char *elevator) if (!v->vdev_wholedisk && strncmp(device, "dm-", 3) != 0) return; - /* Skip devices without schedulers (loop, ram, dm, etc) */ - if (!q->elevator || !blk_queue_stackable(q)) - return; - /* Leave existing scheduler when set to "none" */ if ((strncmp(elevator, "none", 4) == 0) && (strlen(elevator) == 4)) return; + /* + * The elevator_change() function was available in kernels from + * 2.6.36 to 4.11. When not available fall back to using the user + * mode helper functionality to set the elevator via sysfs. This + * requires /bin/echo and sysfs to be mounted which may not be true + * early in the boot process. + */ #ifdef HAVE_ELEVATOR_CHANGE error = elevator_change(q, elevator); #else - /* - * For pre-2.6.36 kernels elevator_change() is not available. - * Therefore we fall back to using a usermodehelper to echo the - * elevator into sysfs; This requires /bin/echo and sysfs to be - * mounted which may not be true early in the boot process. - */ #define SET_SCHEDULER_CMD \ "exec 0/sys/block/%s/queue/scheduler " \ @@ -198,9 +195,10 @@ vdev_elevator_switch(vdev_t *v, char *elevator) error = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC); strfree(argv[2]); #endif /* HAVE_ELEVATOR_CHANGE */ - if (error) - printk("ZFS: Unable to set \"%s\" scheduler for %s (%s): %d\n", + if (error) { + zfs_dbgmsg("Unable to set \"%s\" scheduler for %s (%s): %d\n", elevator, v->vdev_path, device, error); + } } /*