Scheduling module to introduce a fixed delay into the I/O path.

sys/geom/sched/gs_delay.c

@@ -0,0 +1,265 @@
+/*-
+ * Copyright (c) 2015 Netflix, Inc.
+ *
+ * Derived from gs_rr.c:
+ * Copyright (c) 2009-2010 Fabio Checconi
+ * Copyright (c) 2009-2010 Luigi Rizzo, Universita` di Pisa
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * $Id$
+ * $FreeBSD$
+ *
+ * A simple scheduler that just delays certain transactions by a certain
+ * amount. We collect all the transactions that are 'done' and put them on
+ * a queue. The queue is run through every so often and the transactions that
+ * have taken longer than the threshold delay are completed.
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/kernel.h>
+#include <sys/bio.h>
+#include <sys/callout.h>
+#include <sys/malloc.h>
+#include <sys/module.h>
+#include <sys/proc.h>
+#include <sys/queue.h>
+#include <sys/sbuf.h>
+#include <sys/sysctl.h>
+#include "gs_scheduler.h"
+
+/* Useful constants */
+#define BTFRAC_1US 18446744073709ULL	/* 2^64 / 1000000 */
+
+/* list of scheduler instances */
+LIST_HEAD(g_scheds, g_delay_softc);
+
+/*
+ * Per device descriptor, holding the Round Robin list of queues
+ * accessing the disk, a reference to the geom, and the timer.
+ */
+struct g_delay_softc {
+	struct g_geom	*sc_geom;
+
+	struct bio_queue_head sc_bioq;	/* queue of pending requests */
+	struct callout	sc_wait;	/* timer for completing with delays */
+
+	/* Statistics */
+	int		sc_in_flight;	/* requests in the driver */
+};
+
+/*
+ * parameters, config and stats
+ */
+struct g_delay_params {
+	uint64_t io;
+	int	bypass;			/* bypass scheduling */
+	int	units;			/* how many instances */
+	int	latency;		/* How big a latncy are hoping for */
+};
+
+static struct g_delay_params me = {
+	.bypass = 0,
+	.units = 0,
+	.latency = 0,
+	.io = 0,
+};
+struct g_delay_params *gs_delay_me = &me;
+
+SYSCTL_DECL(_kern_geom_sched);
+static SYSCTL_NODE(_kern_geom_sched, OID_AUTO, delay, CTLFLAG_RW, 0,
+    "GEOM_SCHED DELAY stuff");
+SYSCTL_INT(_kern_geom_sched_delay, OID_AUTO, bypass, CTLFLAG_RD,
+    &me.bypass, 0, "Scheduler bypass");
+SYSCTL_INT(_kern_geom_sched_delay, OID_AUTO, units, CTLFLAG_RD,
+    &me.units, 0, "Scheduler instances");
+SYSCTL_INT(_kern_geom_sched_delay, OID_AUTO, latency, CTLFLAG_RW,
+    &me.latency, 0, "Minimum latency for requests, in microseconds (1/hz resolution)");
+SYSCTL_QUAD(_kern_geom_sched_delay, OID_AUTO, io, CTLFLAG_RW,
+    &me.io, 0, "I/Os delayed\n");
+
+static int
+g_delay_init_class(void *data, void *priv)
+{
+	return (0);
+}
+
+static void
+g_delay_fini_class(void *data, void *priv)
+{
+}
+
+/*
+ * Called on a request arrival, timeout or completion.
+ * Try to serve a request among those queued.
+ */
+static struct bio *
+g_delay_next(void *data, int force)
+{
+	struct g_delay_softc *sc = data;
+	struct bio *bp;
+	struct bintime bt;
+
+	bp = bioq_first(&sc->sc_bioq);
+	if (bp == NULL)
+		return (NULL);
+
+	/*
+	 * If the time isn't yet ripe for this bp to be let loose,
+	 * then the time isn't ripe for any of its friends either
+	 * since we insert in-order. Terminate if the bio hasn't
+	 * aged appropriately. Note that there's pathology here
+	 * such that we may be up to one tick early in releasing
+	 * this I/O. We could implement this up to a tick late too
+	 * but choose not to.
+	 */
+	getbinuptime(&bt);	/* BIO's bio_t0 is uptime */
+	if (bintime_cmp(&bp->bio_t0, &bt, >))
+		return (NULL);
+	me.io++;
+	
+	/*
+	 * The bp has mellowed enough, let it through and update stats.
+	 * If there's others, we'll catch them next time we get called.
+	 */
+	sc->sc_in_flight++;
+
+	bp = bioq_takefirst(&sc->sc_bioq);
+	return (bp);
+}
+
+/*
+ * Called when a real request for disk I/O arrives.
+ * Locate the queue associated with the client.
+ * If the queue is the one we are anticipating for, reset its timeout;
+ * if the queue is not in the round robin list, insert it in the list.
+ * On any error, do not queue the request and return -1, the caller
+ * will take care of this request.
+ */
+static int
+g_delay_start(void *data, struct bio *bp)
+{
+	struct g_delay_softc *sc = data;
+
+	if (me.bypass)
+		return (-1);	/* bypass the scheduler */
+
+	bp->bio_caller1 = sc;
+	getbinuptime(&bp->bio_t0);	/* BIO's bio_t0 is uptime */
+	bintime_addx(&bp->bio_t0, BTFRAC_1US * me.latency);
+
+	/*
+	 * Keep the I/Os ordered. Lower layers will reorder as we release them down.
+	 * We rely on this in g_delay_next() so that we delay all things equally. Even
+	 * if we move to multiple queues to push stuff down the stack, we'll want to
+	 * insert in order and let the lower layers do whatever reordering they want.
+	 */
+	bioq_insert_tail(&sc->sc_bioq, bp);
+
+	return (0);
+}
+
+static void
+g_delay_timeout(void *data)
+{
+	struct g_delay_softc *sc = data;
+	
+	g_sched_lock(sc->sc_geom);
+	g_sched_dispatch(sc->sc_geom);
+	g_sched_unlock(sc->sc_geom);
+	callout_reset(&sc->sc_wait, 1, g_delay_timeout, sc);
+}
+
+/*
+ * Module glue: allocate descriptor, initialize its fields.
+ */
+static void *
+g_delay_init(struct g_geom *geom)
+{
+	struct g_delay_softc *sc;
+
+	/* XXX check whether we can sleep */
+	sc = malloc(sizeof *sc, M_GEOM_SCHED, M_NOWAIT | M_ZERO);
+	sc->sc_geom = geom;
+	bioq_init(&sc->sc_bioq);
+	callout_init(&sc->sc_wait, CALLOUT_MPSAFE);
+	callout_reset(&sc->sc_wait, 1, g_delay_timeout, sc);
+	me.units++;
+
+	return (sc);
+}
+
+/*
+ * Module glue -- drain the callout structure, destroy the
+ * hash table and its element, and free the descriptor.
+ */
+static void
+g_delay_fini(void *data)
+{
+	struct g_delay_softc *sc = data;
+
+	/* We're force drained before getting here */
+
+	/* Kick out timers */
+	callout_drain(&sc->sc_wait);
+	me.units--;
+	free(sc, M_GEOM_SCHED);
+}
+
+/*
+ * Called when the request under service terminates.
+ * Start the anticipation timer if needed.
+ */
+static void
+g_delay_done(void *data, struct bio *bp)
+{
+	struct g_delay_softc *sc = data;
+
+	sc->sc_in_flight--;
+
+	g_sched_dispatch(sc->sc_geom);
+}
+
+static void
+g_delay_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
+    struct g_consumer *cp, struct g_provider *pp)
+{
+}
+
+static struct g_gsched g_delay = {
+	.gs_name = "delay",
+	.gs_priv_size = 0,
+	.gs_init = g_delay_init,
+	.gs_fini = g_delay_fini,
+	.gs_start = g_delay_start,
+	.gs_done = g_delay_done,
+	.gs_next = g_delay_next,
+	.gs_dumpconf = g_delay_dumpconf,
+	.gs_init_class = g_delay_init_class,
+	.gs_fini_class = g_delay_fini_class,
+};
+
+DECLARE_GSCHED_MODULE(delay, &g_delay);

sys/modules/geom/geom_sched/Makefile

@@ -1,5 +1,5 @@
 # $FreeBSD$
 
-SUBDIR=	gs_sched gsched_rr
+SUBDIR=	gs_sched gsched_rr gsched_delay
 
 .include <bsd.subdir.mk>

sys/modules/geom/geom_sched/gsched_delay/Makefile

@@ -0,0 +1,7 @@
+# $FreeBSD$
+
+KMOD=   gsched_delay
+SRCS=   gs_delay.c
+
+# ../Makefile.inc automatically included
+.include <bsd.kmod.mk>