MFC r275568:

Count consecutive read requests as blocking in CTL for files and ZVOLs.

Technically read requests can be executed in any order or simultaneously
since they are not changing any data.  But ZFS prefetcher goes crasy when
it receives consecutive requests from different threads.  Since prefetcher
works on level of separate blocks, instead of two consecutive 128K requests
it may receive 32 8K requests in mixed order.

This patch is more workaround then a real fix, and it does not fix all of
prefetcher problems, but it improves sequential read speed by 3-4x times
in some configurations.  On the other side it may hurt performance if
some backing store has no prefetch, that is why it is disabled by default
for raw devices.

6 files changed, 70 insertions, 16 deletions

diff --git a/sys/cam/ctl/ctl.c b/sys/cam/ctl/ctl.c
index b4354f4..b9ec2ad 100644
--- a/sys/cam/ctl/ctl.c
+++ b/sys/cam/ctl/ctl.c
@@ -435,7 +435,9 @@ static int ctl_inquiry_evpd_lbp(struct ctl_scsiio *ctsio, int alloc_len);
 static int ctl_inquiry_evpd(struct ctl_scsiio *ctsio);
 static int ctl_inquiry_std(struct ctl_scsiio *ctsio);
 static int ctl_get_lba_len(union ctl_io *io, uint64_t *lba, uint64_t *len);
-static ctl_action ctl_extent_check(union ctl_io *io1, union ctl_io *io2);
+static ctl_action ctl_extent_check(union ctl_io *io1, union ctl_io *io2,
+    bool seq);
+static ctl_action ctl_extent_check_seq(union ctl_io *io1, union ctl_io *io2);
 static ctl_action ctl_check_for_blockage(struct ctl_lun *lun,
     union ctl_io *pending_io, union ctl_io *ooa_io);
 static ctl_action ctl_check_ooa(struct ctl_lun *lun, union ctl_io *pending_io,
@@ -4592,6 +4594,17 @@ ctl_alloc_lun(struct ctl_softc *ctl_softc, struct ctl_lun *ctl_lun,
 	if (value != NULL && strcmp(value, "on") == 0)
 		lun->flags |= CTL_LUN_READONLY;
 
+	lun->serseq = CTL_LUN_SERSEQ_OFF;
+	if (be_lun->flags & CTL_LUN_FLAG_SERSEQ_READ)
+		lun->serseq = CTL_LUN_SERSEQ_READ;
+	value = ctl_get_opt(&be_lun->options, "serseq");
+	if (value != NULL && strcmp(value, "on") == 0)
+		lun->serseq = CTL_LUN_SERSEQ_ON;
+	else if (value != NULL && strcmp(value, "read") == 0)
+		lun->serseq = CTL_LUN_SERSEQ_READ;
+	else if (value != NULL && strcmp(value, "off") == 0)
+		lun->serseq = CTL_LUN_SERSEQ_OFF;
+
 	lun->ctl_softc = ctl_softc;
 	TAILQ_INIT(&lun->ooa_queue);
 	TAILQ_INIT(&lun->blocked_queue);
@@ -10754,15 +10767,15 @@ ctl_get_lba_len(union ctl_io *io, uint64_t *lba, uint64_t *len)
 }
 
 static ctl_action
-ctl_extent_check_lba(uint64_t lba1, uint64_t len1, uint64_t lba2, uint64_t len2)
+ctl_extent_check_lba(uint64_t lba1, uint64_t len1, uint64_t lba2, uint64_t len2,
+    bool seq)
 {
 	uint64_t endlba1, endlba2;
 
-	endlba1 = lba1 + len1 - 1;
+	endlba1 = lba1 + len1 - (seq ? 0 : 1);
 	endlba2 = lba2 + len2 - 1;
 
-	if ((endlba1 < lba2)
-	 || (endlba2 < lba1))
+	if ((endlba1 < lba2) || (endlba2 < lba1))
 		return (CTL_ACTION_PASS);
 	else
 		return (CTL_ACTION_BLOCK);
@@ -10801,23 +10814,39 @@ ctl_extent_check_unmap(union ctl_io *io, uint64_t lba2, uint64_t len2)
 }
 
 static ctl_action
-ctl_extent_check(union ctl_io *io1, union ctl_io *io2)
+ctl_extent_check(union ctl_io *io1, union ctl_io *io2, bool seq)
 {
 	uint64_t lba1, lba2;
 	uint64_t len1, len2;
 	int retval;
 
-	if (ctl_get_lba_len(io1, &lba1, &len1) != 0)
+	if (ctl_get_lba_len(io2, &lba2, &len2) != 0)
 		return (CTL_ACTION_ERROR);
 
-	retval = ctl_extent_check_unmap(io2, lba1, len1);
+	retval = ctl_extent_check_unmap(io1, lba2, len2);
 	if (retval != CTL_ACTION_ERROR)
 		return (retval);
 
+	if (ctl_get_lba_len(io1, &lba1, &len1) != 0)
+		return (CTL_ACTION_ERROR);
+
+	return (ctl_extent_check_lba(lba1, len1, lba2, len2, seq));
+}
+
+static ctl_action
+ctl_extent_check_seq(union ctl_io *io1, union ctl_io *io2)
+{
+	uint64_t lba1, lba2;
+	uint64_t len1, len2;
+
+	if (ctl_get_lba_len(io1, &lba1, &len1) != 0)
+		return (CTL_ACTION_ERROR);
 	if (ctl_get_lba_len(io2, &lba2, &len2) != 0)
 		return (CTL_ACTION_ERROR);
 
-	return (ctl_extent_check_lba(lba1, len1, lba2, len2));
+	if (lba1 + len1 == lba2)
+		return (CTL_ACTION_BLOCK);
+	return (CTL_ACTION_PASS);
 }
 
 static ctl_action
@@ -10906,12 +10935,18 @@ ctl_check_for_blockage(struct ctl_lun *lun, union ctl_io *pending_io,
 	case CTL_SER_BLOCK:
 		return (CTL_ACTION_BLOCK);
 	case CTL_SER_EXTENT:
-		return (ctl_extent_check(pending_io, ooa_io));
+		return (ctl_extent_check(ooa_io, pending_io,
+		    (lun->serseq == CTL_LUN_SERSEQ_ON)));
 	case CTL_SER_EXTENTOPT:
 		if ((lun->mode_pages.control_page[CTL_PAGE_CURRENT].queue_flags
 		    & SCP_QUEUE_ALG_MASK) != SCP_QUEUE_ALG_UNRESTRICTED)
-			return (ctl_extent_check(pending_io, ooa_io));
-		/* FALLTHROUGH */
+			return (ctl_extent_check(ooa_io, pending_io,
+			    (lun->serseq == CTL_LUN_SERSEQ_ON)));
+		return (CTL_ACTION_PASS);
+	case CTL_SER_EXTENTSEQ:
+		if (lun->serseq != CTL_LUN_SERSEQ_OFF)
+			return (ctl_extent_check_seq(ooa_io, pending_io));
+		return (CTL_ACTION_PASS);
 	case CTL_SER_PASS:
 		return (CTL_ACTION_PASS);
 	case CTL_SER_BLOCKOPT:
@@ -12442,7 +12477,7 @@ ctl_cmd_pattern_match(struct ctl_scsiio *ctsio, struct ctl_error_desc *desc)
 			return (CTL_LUN_PAT_NONE);
 
 		action = ctl_extent_check_lba(lba1, len1, desc->lba_range.lba,
-					      desc->lba_range.len);
+					      desc->lba_range.len, FALSE);
 		/*
 		 * A "pass" means that the LBA ranges don't overlap, so
 		 * this doesn't match the user's range criteria.
diff --git a/sys/cam/ctl/ctl_backend.h b/sys/cam/ctl/ctl_backend.h
index f32d120..77975f9 100644
--- a/sys/cam/ctl/ctl_backend.h
+++ b/sys/cam/ctl/ctl_backend.h
@@ -85,7 +85,8 @@ typedef enum {
 	CTL_LUN_FLAG_DEVID		= 0x20,
 	CTL_LUN_FLAG_DEV_TYPE		= 0x40,
 	CTL_LUN_FLAG_UNMAP		= 0x80,
-	CTL_LUN_FLAG_OFFLINE		= 0x100
+	CTL_LUN_FLAG_OFFLINE		= 0x100,
+	CTL_LUN_FLAG_SERSEQ_READ	= 0x200
 } ctl_backend_lun_flags;
 
 #ifdef _KERNEL
diff --git a/sys/cam/ctl/ctl_backend_block.c b/sys/cam/ctl/ctl_backend_block.c
index 8f7c5d4..e3f52d7 100644
--- a/sys/cam/ctl/ctl_backend_block.c
+++ b/sys/cam/ctl/ctl_backend_block.c
@@ -2207,6 +2207,8 @@ ctl_be_block_create(struct ctl_be_block_softc *softc, struct ctl_lun_req *req)
 		be_lun->ctl_be_lun.flags |= CTL_LUN_FLAG_OFFLINE;
 	if (unmap)
 		be_lun->ctl_be_lun.flags |= CTL_LUN_FLAG_UNMAP;
+	if (be_lun->dispatch != ctl_be_block_dispatch_dev)
+		be_lun->ctl_be_lun.flags |= CTL_LUN_FLAG_SERSEQ_READ;
 	be_lun->ctl_be_lun.be_lun = be_lun;
 	be_lun->ctl_be_lun.maxlba = (be_lun->size_blocks == 0) ?
 	    0 : (be_lun->size_blocks - 1);
diff --git a/sys/cam/ctl/ctl_private.h b/sys/cam/ctl/ctl_private.h
index 351b7f8..7bedf10 100644
--- a/sys/cam/ctl/ctl_private.h
+++ b/sys/cam/ctl/ctl_private.h
@@ -97,6 +97,7 @@ typedef enum {
 	CTL_SER_BLOCKOPT,
 	CTL_SER_EXTENT,
 	CTL_SER_EXTENTOPT,
+	CTL_SER_EXTENTSEQ,
 	CTL_SER_PASS,
 	CTL_SER_SKIP
 } ctl_serialize_action;
@@ -183,6 +184,12 @@ typedef enum {
 } ctl_lun_flags;
 
 typedef enum {
+	CTL_LUN_SERSEQ_OFF,
+	CTL_LUN_SERSEQ_READ,
+	CTL_LUN_SERSEQ_ON
+} ctl_lun_serseq;
+
+typedef enum {
 	CTLBLOCK_FLAG_NONE	= 0x00,
 	CTLBLOCK_FLAG_INVALID	= 0x01
 } ctlblock_flags;
@@ -386,6 +393,7 @@ struct ctl_lun {
 	struct ctl_id			target;
 	uint64_t			lun;
 	ctl_lun_flags			flags;
+	ctl_lun_serseq			serseq;
 	STAILQ_HEAD(,ctl_error_desc)	error_list;
 	uint64_t			error_serial;
 	struct ctl_softc		*ctl_softc;
diff --git a/sys/cam/ctl/ctl_ser_table.c b/sys/cam/ctl/ctl_ser_table.c
index d3693ce..ee2d019 100644
--- a/sys/cam/ctl/ctl_ser_table.c
+++ b/sys/cam/ctl/ctl_ser_table.c
@@ -59,12 +59,13 @@
 #define	bO	CTL_SER_BLOCKOPT	/* Optional block */
 #define	xT	CTL_SER_EXTENT		/* Extent check */
 #define	xO	CTL_SER_EXTENTOPT	/* Optional extent check */
+#define	xS	CTL_SER_EXTENTSEQ	/* Sequential extent check */
 
 static ctl_serialize_action
 ctl_serialize_table[CTL_SERIDX_COUNT][CTL_SERIDX_COUNT] = {
 /**>IDX_ :: 2nd:TUR RD  WRT UNM MDSN MDSL RQSN INQ RDCP RES LSNS FMT STR*/
 /*TUR     */{   pS, pS, pS, pS, bK,  bK,  bK,  pS, pS,  bK, pS,  bK, bK},
-/*READ    */{   pS, pS, xT, bO, bK,  bK,  bK,  pS, pS,  bK, pS,  bK, bK},
+/*READ    */{   pS, xS, xT, bO, bK,  bK,  bK,  pS, pS,  bK, pS,  bK, bK},
 /*WRITE   */{   pS, xT, xT, bO, bK,  bK,  bK,  pS, pS,  bK, pS,  bK, bK},
 /*UNMAP   */{   pS, xO, xO, pS, bK,  bK,  bK,  pS, pS,  bK, pS,  bK, bK},
 /*MD_SNS  */{   bK, bK, bK, bK, pS,  bK,  bK,  pS, pS,  bK, pS,  bK, bK},
diff --git a/usr.sbin/ctladm/ctladm.8 b/usr.sbin/ctladm/ctladm.8
index 21b1946..e23e743 100644
--- a/usr.sbin/ctladm/ctladm.8
+++ b/usr.sbin/ctladm/ctladm.8
@@ -34,7 +34,7 @@
 .\" $Id: //depot/users/kenm/FreeBSD-test2/usr.sbin/ctladm/ctladm.8#3 $
 .\" $FreeBSD$
 .\"
-.Dd November 5, 2014
+.Dd December 6, 2014
 .Dt CTLADM 8
 .Os
 .Sh NAME
@@ -995,6 +995,13 @@ command sequence order shall be explicitly handled by the application
 client through the selection of appropriate commands and task attributes.
 The default value is "restricted".  It improves data integrity, but may
 introduce some additional delays.
+.It Va serseq
+Set to "on" to serialize conseсutive reads/writes.
+Set to "read" to serialize conseсutive reads.
+Set to "off" to allow them be issued in parallel.
+Parallel issue of consecutive operations may confuse logic of the
+backing file system, hurting performance; but it may improve performance
+of backing stores without prefetch/write-back.
 .It Va rpm
 Specifies medium rotation rate of the device: 0 -- not reported,
 1 -- non-rotating (SSD), >1024 -- value in revolutions per minute.