Yield the cpu in the kernel while iterating the list of the

vnodes belonging to the mountpoint. Also, yield when in the
softdep_process_worklist() even when we are not going to sleep due to
buffer drain.

It is believed that the ULE fixed the problem [1], but the yielding
seems to be needed at least for the 4BSD case.

Discussed:	on stable@, with bde
Reviewed by:	tegge, jeff [1]
MFC after:	2 weeks

3 files changed, 9 insertions, 0 deletions

diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 0f829a9..3961022 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -2008,6 +2008,12 @@ __mnt_vnode_next(struct vnode **mvp, struct mount *mp)
 	mtx_assert(MNT_MTX(mp), MA_OWNED);
 
 	KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
+	if ((*mvp)->v_yield++ == 500) {
+		MNT_IUNLOCK(mp);
+		(*mvp)->v_yield = 0;
+		uio_yield();
+		MNT_ILOCK(mp);
+	}
 	vp = TAILQ_NEXT(*mvp, v_nmntvnodes);
 	while (vp != NULL && vp->v_type == VMARKER)
 		vp = TAILQ_NEXT(vp, v_nmntvnodes);
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index a1ec516..ba23b18 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -124,6 +124,7 @@ struct vnode {
 		struct socket	*vu_socket;	/* v unix domain net (VSOCK) */
 		struct cdev	*vu_cdev; 	/* v device (VCHR, VBLK) */
 		struct fifoinfo	*vu_fifoinfo;	/* v fifo (VFIFO) */
+		int		vu_yield;	/*   yield count (VMARKER) */
 	} v_un;
 
 	/*
@@ -178,6 +179,7 @@ struct vnode {
 #define	v_socket	v_un.vu_socket
 #define	v_rdev		v_un.vu_cdev
 #define	v_fifoinfo	v_un.vu_fifoinfo
+#define	v_yield		v_un.vu_yield
 
 /* XXX: These are temporary to avoid a source sweep at this time */
 #define v_object	v_bufobj.bo_object
diff --git a/sys/ufs/ffs/ffs_softdep.c b/sys/ufs/ffs/ffs_softdep.c
index 7cb7b40..255723c 100644
--- a/sys/ufs/ffs/ffs_softdep.c
+++ b/sys/ufs/ffs/ffs_softdep.c
@@ -857,6 +857,7 @@ softdep_process_worklist(mp, full)
 		 */
 		if (loopcount++ % 128 == 0) {
 			FREE_LOCK(&lk);
+			uio_yield();
 			bwillwrite();
 			ACQUIRE_LOCK(&lk);
 		}