From 7bd04f2d7d99780f190d4027e6e81fc0df11ba95 Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Fri, 5 Oct 2012 10:39:35 -0700 Subject: [PATCH] Set default zvol elevator to noop It doesn't make sense for a zvol to use the default system I/O scheduler because it is a virtual device. Therefore, we change the default scheduler to 'noop' for zvols provided that the elevator_change() function is available. This interface has been available since Linux 2.6.36 and appears in the RHEL 6.x kernels. We deliberately do not implement the method for older kernels because it was racy and could result in system crashes. It's better to simply manually tune the scheduler for these kernels. Signed-off-by: Brian Behlendorf Closes #1017 --- module/zfs/zvol.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c index b07476c..c3bd25c 100644 --- a/module/zfs/zvol.c +++ b/module/zfs/zvol.c @@ -1159,6 +1159,7 @@ static zvol_state_t * zvol_alloc(dev_t dev, const char *name) { zvol_state_t *zv; + int error = 0; zv = kmem_zalloc(sizeof (zvol_state_t), KM_SLEEP); if (zv == NULL) @@ -1168,6 +1169,15 @@ zvol_alloc(dev_t dev, const char *name) if (zv->zv_queue == NULL) goto out_kmem; +#ifdef HAVE_ELEVATOR_CHANGE + error = elevator_change(zv->zv_queue, "noop"); +#endif /* HAVE_ELEVATOR_CHANGE */ + if (error) { + printk("ZFS: Unable to set \"%s\" scheduler for zvol %s: %d\n", + "noop", name, error); + goto out_queue; + } + #ifdef HAVE_BLK_QUEUE_FLUSH blk_queue_flush(zv->zv_queue, VDEV_REQ_FLUSH | VDEV_REQ_FUA); #else -- 1.8.3.1