[src/trunk]: src/sys/rump/librump/rumpkern Implement softint_schedule_cpu() f...

[pooka <pooka%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/3cab2268c69f
branches:  trunk
changeset: 805704:3cab2268c69f
user:      pooka <pooka%NetBSD.org@localhost>
date:      Wed Jan 14 18:46:38 2015 +0000

description:
Implement softint_schedule_cpu() for rump kernels.

While distributing processing all over the place is not relevant for
high-performance rump kernel I/O stacks (and downright counterproductive),
the mechanism is used e.g. to reach a quiescent state when detaching
an interface, and therefore a semantically correct implementation is
required.

Fixes at least an uncommon race in the ifconfig destroy case.
reported & patch tested by Justin Cormack.

diffstat:

 sys/rump/librump/rumpkern/intr.c |  112 ++++++++++++++++++++++++++++++++++++--
 1 files changed, 104 insertions(+), 8 deletions(-)

diffs (180 lines):

diff -r a7a8d731ba4d -r 3cab2268c69f sys/rump/librump/rumpkern/intr.c
--- a/sys/rump/librump/rumpkern/intr.c  Wed Jan 14 17:45:27 2015 +0000
+++ b/sys/rump/librump/rumpkern/intr.c  Wed Jan 14 18:46:38 2015 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: intr.c,v 1.46 2014/06/22 20:09:19 pooka Exp $  */
+/*     $NetBSD: intr.c,v 1.47 2015/01/14 18:46:38 pooka Exp $  */
 
 /*
  * Copyright (c) 2008-2010 Antti Kantee.  All Rights Reserved.
@@ -26,7 +26,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: intr.c,v 1.46 2014/06/22 20:09:19 pooka Exp $");
+__KERNEL_RCSID(0, "$NetBSD: intr.c,v 1.47 2015/01/14 18:46:38 pooka Exp $");
 
 #include <sys/param.h>
 #include <sys/atomic.h>
@@ -62,8 +62,10 @@
 struct softint_percpu {
        struct softint *sip_parent;
        bool sip_onlist;
+       bool sip_onlist_cpu;
 
-       LIST_ENTRY(softint_percpu) sip_entries;
+       LIST_ENTRY(softint_percpu) sip_entries;         /* scheduled */
+       TAILQ_ENTRY(softint_percpu) sip_entries_cpu;    /* to be scheduled */
 };
 
 struct softint_lev {
@@ -71,6 +73,11 @@
        LIST_HEAD(, softint_percpu) si_pending;
 };
 
+static TAILQ_HEAD(, softint_percpu) sicpupending \
+    = TAILQ_HEAD_INITIALIZER(sicpupending);
+static struct rumpuser_mtx *sicpumtx;
+static struct rumpuser_cv *sicpucv;
+
 kcondvar_t lbolt; /* Oh Kath Ra */
 
 static u_int ticks;
@@ -183,6 +190,51 @@
        panic("sithread unreachable");
 }
 
+/*
+ * Helper for softint_schedule_cpu()
+ */
+static void
+sithread_cpu_bouncer(void *arg)
+{
+       struct lwp *me;
+
+       me = curlwp;
+       me->l_pflag |= LP_BOUND;
+
+       rump_unschedule();
+       for (;;) {
+               struct softint_percpu *sip;
+               struct softint *si;
+               struct cpu_info *ci;
+               unsigned int cidx;
+
+               rumpuser_mutex_enter_nowrap(sicpumtx);
+               while (TAILQ_EMPTY(&sicpupending)) {
+                       rumpuser_cv_wait_nowrap(sicpucv, sicpumtx);
+               }
+               sip = TAILQ_FIRST(&sicpupending);
+               TAILQ_REMOVE(&sicpupending, sip, sip_entries_cpu);
+               sip->sip_onlist_cpu = false;
+               rumpuser_mutex_exit(sicpumtx);
+
+               /*
+                * ok, now figure out which cpu we need the softint to
+                * be handled on
+                */
+               si = sip->sip_parent;
+               cidx = sip - si->si_entry;
+               ci = cpu_lookup(cidx);
+               me->l_target_cpu = ci;
+
+               /* schedule ourselves there, and then schedule the softint */
+               rump_schedule();
+               KASSERT(curcpu() == ci);
+               softint_schedule(si);
+               rump_unschedule();
+       }
+       panic("sithread_cpu_bouncer unreasonable");
+}
+
 static kmutex_t sithr_emtx;
 static unsigned int sithr_est;
 static int sithr_canest;
@@ -273,6 +325,13 @@
        if ((rv = kthread_create(PRI_NONE, KTHREAD_MPSAFE,
            ci, doclock, NULL, NULL, "rumpclk%d", ci->ci_index)) != 0)
                panic("clock thread creation failed: %d", rv);
+
+       /* not one either, but at least a softint helper */
+       rumpuser_mutex_init(&sicpumtx, RUMPUSER_MTX_SPIN);
+       rumpuser_cv_init(&sicpucv);
+       if ((rv = kthread_create(PRI_NONE, KTHREAD_MPSAFE,
+           NULL, sithread_cpu_bouncer, NULL, NULL, "sipbnc")) != 0)
+               panic("softint cpu bouncer creation failed: %d", rv);
 }
 
 void *
@@ -300,6 +359,13 @@
        return si;
 }
 
+static struct softint_percpu *
+sitosip(struct softint *si, struct cpu_info *ci)
+{
+
+       return &si->si_entry[ci->ci_index];
+}
+
 /*
  * Soft interrupts bring two choices.  If we are running with thread
  * support enabled, defer execution, otherwise execute in place.
@@ -310,7 +376,7 @@
 {
        struct softint *si = arg;
        struct cpu_info *ci = curcpu();
-       struct softint_percpu *sip = &si->si_entry[ci->ci_index];
+       struct softint_percpu *sip = sitosip(si, ci);
        struct cpu_data *cd = &ci->ci_data;
        struct softint_lev *si_lvl = cd->cpu_softcpu;
 
@@ -325,14 +391,44 @@
        }
 }
 
+/*
+ * Like softint_schedule(), except schedule softint to be handled on
+ * the core designated by ci_tgt instead of the core the call is made on.
+ *
+ * Unlike softint_schedule(), the performance is not important
+ * (unless ci_tgt == curcpu): high-performance rump kernel I/O stacks
+ * should arrange data to already be on the right core at the driver
+ * layer.
+ */
 void
-softint_schedule_cpu(void *arg, struct cpu_info *ci)
+softint_schedule_cpu(void *arg, struct cpu_info *ci_tgt)
 {
+       struct softint *si = arg;
+       struct cpu_info *ci_cur = curcpu();
+       struct softint_percpu *sip;
+
+       KASSERT(rump_threads);
+
+       /* preferred case (which can be optimized some day) */
+       if (ci_cur == ci_tgt) {
+               softint_schedule(si);
+               return;
+       }
+
        /*
-        * TODO: implement this properly
+        * no?  then it's softint turtles all the way down
         */
-       KASSERT(curcpu() == ci);
-       softint_schedule(arg);
+
+       sip = sitosip(si, ci_tgt);
+       rumpuser_mutex_enter_nowrap(sicpumtx);
+       if (sip->sip_onlist_cpu) {
+               rumpuser_mutex_exit(sicpumtx);
+               return;
+       }
+       TAILQ_INSERT_TAIL(&sicpupending, sip, sip_entries_cpu);
+       sip->sip_onlist_cpu = true;
+       rumpuser_cv_signal(sicpucv);
+       rumpuser_mutex_exit(sicpumtx);
 }
 
 /*