Module Name: src
Committed By: pooka
Date: Thu May 2 20:33:54 UTC 2013
Modified Files:
src/lib/librumpuser: rumpuser_pth.c
src/sys/rump/librump/rumpkern: locks.c
Log Message:
Retry enabling spin mutexes. We should be able to avoid poking the
scheduler by just making wakeup from cv_wait() honor the same locking
order as when a spin mutex is acquired though mutex_enter().
*fingers crossed*
To generate a diff of this commit:
cvs rdiff -u -r1.23 -r1.24 src/lib/librumpuser/rumpuser_pth.c
cvs rdiff -u -r1.60 -r1.61 src/sys/rump/librump/rumpkern/locks.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/lib/librumpuser/rumpuser_pth.c
diff -u src/lib/librumpuser/rumpuser_pth.c:1.23 src/lib/librumpuser/rumpuser_pth.c:1.24
--- src/lib/librumpuser/rumpuser_pth.c:1.23 Thu May 2 19:14:59 2013
+++ src/lib/librumpuser/rumpuser_pth.c Thu May 2 20:33:54 2013
@@ -1,4 +1,4 @@
-/* $NetBSD: rumpuser_pth.c,v 1.23 2013/05/02 19:14:59 pooka Exp $ */
+/* $NetBSD: rumpuser_pth.c,v 1.24 2013/05/02 20:33:54 pooka Exp $ */
/*
* Copyright (c) 2007-2010 Antti Kantee. All Rights Reserved.
@@ -28,7 +28,7 @@
#include "rumpuser_port.h"
#if !defined(lint)
-__RCSID("$NetBSD: rumpuser_pth.c,v 1.23 2013/05/02 19:14:59 pooka Exp $");
+__RCSID("$NetBSD: rumpuser_pth.c,v 1.24 2013/05/02 20:33:54 pooka Exp $");
#endif /* !lint */
#include <sys/queue.h>
@@ -378,17 +378,53 @@ rumpuser_cv_destroy(struct rumpuser_cv *
free(cv);
}
+static void
+cv_unschedule(struct rumpuser_mtx *mtx, int *nlocks)
+{
+
+ rumpkern_unsched(nlocks, mtx);
+ mtxexit(mtx);
+}
+
+static void
+cv_reschedule(struct rumpuser_mtx *mtx, int nlocks)
+{
+
+ /*
+ * If the cv interlock is a spin mutex, we must first release
+ * the mutex that was reacquired by pthread_cond_wait(),
+ * acquire the CPU context and only then relock the mutex.
+ * This is to preserve resource allocation order so that
+ * we don't deadlock. Non-spinning mutexes don't have this
+ * problem since they don't use a hold-and-wait approach
+ * to acquiring the mutex wrt the rump kernel CPU context.
+ *
+ * The more optimal solution would be to rework rumpkern_sched()
+ * so that it's possible to tell the scheduler
+ * "if you need to block, drop this lock first", but I'm not
+ * going poking there without some numbers on how often this
+ * path is taken for spin mutexes.
+ */
+ if ((mtx->flags & (RUMPUSER_MTX_SPIN | RUMPUSER_MTX_KMUTEX)) ==
+ (RUMPUSER_MTX_SPIN | RUMPUSER_MTX_KMUTEX)) {
+ NOFAIL_ERRNO(pthread_mutex_unlock(&mtx->pthmtx));
+ rumpkern_sched(nlocks, mtx);
+ rumpuser_mutex_enter_nowrap(mtx);
+ } else {
+ mtxenter(mtx);
+ rumpkern_sched(nlocks, mtx);
+ }
+}
+
void
rumpuser_cv_wait(struct rumpuser_cv *cv, struct rumpuser_mtx *mtx)
{
int nlocks;
cv->nwaiters++;
- rumpkern_unsched(&nlocks, mtx);
- mtxexit(mtx);
+ cv_unschedule(mtx, &nlocks);
NOFAIL_ERRNO(pthread_cond_wait(&cv->pthcv, &mtx->pthmtx));
- mtxenter(mtx);
- rumpkern_sched(nlocks, mtx);
+ cv_reschedule(mtx, nlocks);
cv->nwaiters--;
}
@@ -420,8 +456,7 @@ rumpuser_cv_timedwait(struct rumpuser_cv
clock_gettime(CLOCK_REALTIME, &ts);
cv->nwaiters++;
- rumpkern_unsched(&nlocks, mtx);
- mtxexit(mtx);
+ cv_unschedule(mtx, &nlocks);
ts.tv_sec += sec;
ts.tv_nsec += nsec;
@@ -430,8 +465,8 @@ rumpuser_cv_timedwait(struct rumpuser_cv
ts.tv_nsec -= 1000*1000*1000;
}
rv = pthread_cond_timedwait(&cv->pthcv, &mtx->pthmtx, &ts);
- mtxenter(mtx);
- rumpkern_sched(nlocks, mtx);
+
+ cv_reschedule(mtx, nlocks);
cv->nwaiters--;
ET(rv);
Index: src/sys/rump/librump/rumpkern/locks.c
diff -u src/sys/rump/librump/rumpkern/locks.c:1.60 src/sys/rump/librump/rumpkern/locks.c:1.61
--- src/sys/rump/librump/rumpkern/locks.c:1.60 Tue Apr 30 00:03:53 2013
+++ src/sys/rump/librump/rumpkern/locks.c Thu May 2 20:33:54 2013
@@ -1,4 +1,4 @@
-/* $NetBSD: locks.c,v 1.60 2013/04/30 00:03:53 pooka Exp $ */
+/* $NetBSD: locks.c,v 1.61 2013/05/02 20:33:54 pooka Exp $ */
/*
* Copyright (c) 2007-2011 Antti Kantee. All Rights Reserved.
@@ -26,7 +26,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: locks.c,v 1.60 2013/04/30 00:03:53 pooka Exp $");
+__KERNEL_RCSID(0, "$NetBSD: locks.c,v 1.61 2013/05/02 20:33:54 pooka Exp $");
#include <sys/param.h>
#include <sys/kmem.h>
@@ -113,11 +113,9 @@ mutex_init(kmutex_t *mtx, kmutex_type_t
isspin = 1;
}
-#if 0
/* spin mutex support needs some cpu scheduler rework */
if (isspin)
ruflags |= RUMPUSER_MTX_SPIN;
-#endif
rumpuser_mutex_init((struct rumpuser_mtx **)mtx, ruflags);
ALLOCK(mtx, &mutex_lockops);
}
@@ -144,7 +142,7 @@ mutex_spin_enter(kmutex_t *mtx)
{
WANTLOCK(mtx, false, false);
- rumpuser_mutex_enter(RUMPMTX(mtx));
+ rumpuser_mutex_enter_nowrap(RUMPMTX(mtx));
LOCKED(mtx, false);
}
