Merge GEOM direct dispatch changes from the projects/camlock branch.

When safety requirements are met, it allows to avoid passing I/O requests
to GEOM g_up/g_down thread, executing them directly in the caller context.
That allows to avoid CPU bottlenecks in g_up/g_down threads, plus avoid
several context switches per I/O.

The defined now safety requirements are:
 - caller should not hold any locks and should be reenterable;
 - callee should not depend on GEOM dual-threaded concurency semantics;
 - on the way down, if request is unmapped while callee doesn't support it,
   the context should be sleepable;
 - kernel thread stack usage should be below 50%.

To keep compatibility with GEOM classes not meeting above requirements
new provider and consumer flags added:
 - G_CF_DIRECT_SEND -- consumer code meets caller requirements (request);
 - G_CF_DIRECT_RECEIVE -- consumer code meets callee requirements (done);
 - G_PF_DIRECT_SEND -- provider code meets caller requirements (done);
 - G_PF_DIRECT_RECEIVE -- provider code meets callee requirements (request).
Capable GEOM class can set them, allowing direct dispatch in cases where
it is safe.  If any of requirements are not met, request is queued to
g_up or g_down thread same as before.

Such GEOM classes were reviewed and updated to support direct dispatch:
CONCAT, DEV, DISK, GATE, MD, MIRROR, MULTIPATH, NOP, PART, RAID, STRIPE,
VFS, ZERO, ZFS::VDEV, ZFS::ZVOL, all classes based on g_slice KPI (LABEL,
MAP, FLASHMAP, etc).

To declare direct completion capability disk(9) KPI got new flag equivalent
to G_PF_DIRECT_SEND -- DISKFLAG_DIRECT_COMPLETION.  da(4) and ada(4) disk
drivers got it set now thanks to earlier CAM locking work.

This change more then twice increases peak block storage performance on
systems with manu CPUs, together with earlier CAM locking changes reaching
more then 1 million IOPS (512 byte raw reads from 16 SATA SSDs on 4 HBAs to
256 user-level threads).

Sponsored by:	iXsystems, Inc.
MFC after:	2 months

2 files changed, 12 insertions, 2 deletions

diff --git a/sys/geom/nop/g_nop.c b/sys/geom/nop/g_nop.c
index 0cb0374..e6b44bb 100644
--- a/sys/geom/nop/g_nop.c
+++ b/sys/geom/nop/g_nop.c
@@ -107,6 +107,7 @@ g_nop_start(struct bio *bp)
 	gp = bp->bio_to->geom;
 	sc = gp->softc;
 	G_NOP_LOGREQ(bp, "Request received.");
+	mtx_lock(&sc->sc_lock);
 	switch (bp->bio_cmd) {
 	case BIO_READ:
 		sc->sc_reads++;
@@ -119,6 +120,7 @@ g_nop_start(struct bio *bp)
 		failprob = sc->sc_wfailprob;
 		break;
 	}
+	mtx_unlock(&sc->sc_lock);
 	if (failprob > 0) {
 		u_int rval;
 
@@ -224,6 +226,7 @@ g_nop_create(struct gctl_req *req, struct g_class *mp, struct g_provider *pp,
 	sc->sc_writes = 0;
 	sc->sc_readbytes = 0;
 	sc->sc_wrotebytes = 0;
+	mtx_init(&sc->sc_lock, "gnop lock", NULL, MTX_DEF);
 	gp->softc = sc;
 	gp->start = g_nop_start;
 	gp->orphan = g_nop_orphan;
@@ -232,10 +235,12 @@ g_nop_create(struct gctl_req *req, struct g_class *mp, struct g_provider *pp,
 	gp->dumpconf = g_nop_dumpconf;
 
 	newpp = g_new_providerf(gp, "%s", gp->name);
+	newpp->flags |= G_PF_DIRECT_SEND | G_PF_DIRECT_RECEIVE;
 	newpp->mediasize = size;
 	newpp->sectorsize = secsize;
 
 	cp = g_new_consumer(gp);
+	cp->flags |= G_CF_DIRECT_SEND | G_CF_DIRECT_RECEIVE;
 	error = g_attach(cp, pp);
 	if (error != 0) {
 		gctl_error(req, "Cannot attach to provider %s.", pp->name);
@@ -251,6 +256,7 @@ fail:
 		g_detach(cp);
 	g_destroy_consumer(cp);
 	g_destroy_provider(newpp);
+	mtx_destroy(&sc->sc_lock);
 	g_free(gp->softc);
 	g_destroy_geom(gp);
 	return (error);
@@ -259,10 +265,12 @@ fail:
 static int
 g_nop_destroy(struct g_geom *gp, boolean_t force)
 {
+	struct g_nop_softc *sc;
 	struct g_provider *pp;
 
 	g_topology_assert();
-	if (gp->softc == NULL)
+	sc = gp->softc;
+	if (sc == NULL)
 		return (ENXIO);
 	pp = LIST_FIRST(&gp->provider);
 	if (pp != NULL && (pp->acr != 0 || pp->acw != 0 || pp->ace != 0)) {
@@ -277,8 +285,9 @@ g_nop_destroy(struct g_geom *gp, boolean_t force)
 	} else {
 		G_NOP_DEBUG(0, "Device %s removed.", gp->name);
 	}
-	g_free(gp->softc);
 	gp->softc = NULL;
+	mtx_destroy(&sc->sc_lock);
+	g_free(sc);
 	g_wither_geom(gp, ENXIO);
 
 	return (0);
diff --git a/sys/geom/nop/g_nop.h b/sys/geom/nop/g_nop.h
index da555ec..3e37c05 100644
--- a/sys/geom/nop/g_nop.h
+++ b/sys/geom/nop/g_nop.h
@@ -65,6 +65,7 @@ struct g_nop_softc {
 	uintmax_t	sc_writes;
 	uintmax_t	sc_readbytes;
 	uintmax_t	sc_wrotebytes;
+	struct mtx	sc_lock;
 };
 #endif	/* _KERNEL */