Well, try this hacky patch. It's not correct by any stretches of
imagination, nor am I promising to accept something like it into
Rumprun, but if you can repeat my results, at least we've narrowed down
the problem. In my testing the clock_gettime-to-clock_gettime delay for
a 1ns sleep on KVM is ~8us with this patch.
(btw, the init code might not in correct order as indicated by the
comment, try to hack around it somehow if that happens)
diff --git a/lib/librumpkern_bmktc/Makefile b/lib/librumpkern_bmktc/Makefile
index c368624..0eace29 100644
--- a/lib/librumpkern_bmktc/Makefile
+++ b/lib/librumpkern_bmktc/Makefile
@@ -3,6 +3,7 @@
LIB= rumpkern_bmktc
SRCS+= rump_bmktc.c
+SRCS+= sys_nanosleep.c
RUMPTOP= ${TOPRUMP}
diff --git a/lib/librumpkern_bmktc/sys_nanosleep.c
b/lib/librumpkern_bmktc/sys_nanosleep.c
new file mode 100644
index 0000000..a6dac55
--- /dev/null
+++ b/lib/librumpkern_bmktc/sys_nanosleep.c
@@ -0,0 +1,66 @@
+/*-
+ * Copyright (c) 2016 Antti Kantee. 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 ``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.
+ */
+
+#include <sys/cdefs.h>
+
+#include <sys/param.h>
+#include <sys/errno.h>
+#include <sys/syscall.h>
+#include <sys/syscallargs.h>
+
+#include <rump/rumpuser.h>
+
+#include <rump-sys/kern.h>
+
+static int
+accurate_nanosleep(struct lwp *l, const struct sys___nanosleep50_args *uap,
+ register_t *retval)
+{
+ struct timespec ts;
+
+ copyin(SCARG(uap, rqtp), &ts, sizeof(struct timespec));
+ rumpuser_clock_sleep(RUMPUSER_CLOCK_RELWALL, ts.tv_sec, ts.tv_nsec);
+ return 0;
+}
+
+/*
+ * XXX: undefined if this runs before or after the actual syscalls are
+ * established, but since there's no other convenient way to plug things
+ * in, we hope and we hope.
+ */
+RUMP_COMPONENT(RUMP_COMPONENT_SYSCALL)
+{
+ struct sysent *ent;
+
+ printf("establishing hacky clock syscalls\n");
+
+ ent = rump_sysent + SYS___nanosleep50;
+ KASSERT(ent->sy_call != (sy_call_t *)enosys);
+ ent->sy_call = (sy_call_t *)accurate_nanosleep;
+
+ ent = rump_sysent + SYS_clock_nanosleep;
+ KASSERT(ent->sy_call != (sy_call_t *)enosys);
+ ent->sy_call = (sy_call_t *)accurate_nanosleep;
+}
