Re: xcall while cold == 1

[Masanobu SAITOH <msaitoh%execsw.org@localhost>]

On 2017/12/26 11:59, Masanobu SAITOH wrote:
> On 2017/12/25 20:26, Martin Husemann wrote:
> > On Mon, Dec 25, 2017 at 03:42:06PM +0900, Masanobu SAITOH wrote:
> > >   Is this intended behavior? Is it possible to use xcall while
> > > cold==1?
> >
> > Cold is (as you noted) not the right condition (but pretty close).
> >
> > Xcalls don't really make any sense before cpus have been spun up.
> > In your case it might be good to do the loop checking for SPCF_RUNNING
> > and if <= 1 is found, use the code path for single cpu systems (the
> > current else statatement).
>
> In init_main.c::configure2():
>
> >         cold = 0;       /* clocks are running, we're warm now! */
> >         s = splsched();
> >         curcpu()->ci_schedstate.spc_flags |= SPCF_RUNNING;
> >         splx(s);
> >
> >         /* Boot the secondary processors. */
> >         for (CPU_INFO_FOREACH(cii, ci)) {
> >                 uvm_cpu_attach(ci);
> >         }
> >         mp_online = true;
>
> so checking mp_online is the best, right?
>
> > Martin

Updated diff:
-----------------
Index: kern_softint.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_softint.c,v
retrieving revision 1.44
diff -u -p -r1.44 kern_softint.c
--- kern_softint.c	22 Nov 2017 02:20:21 -0000	1.44
+++ kern_softint.c	26 Dec 2017 07:47:57 -0000
@@ -177,6 +177,7 @@ __KERNEL_RCSID(0, "$NetBSD: kern_softint
 #include <sys/intr.h>
 #include <sys/ipi.h>
 #include <sys/mutex.h>
+#include <sys/kernel.h>
 #include <sys/kthread.h>
 #include <sys/evcnt.h>
 #include <sys/cpu.h>
@@ -430,8 +431,10 @@ softint_disestablish(void *arg)
 	 * it again.  So, we are only looking for handler records with
 	 * SOFTINT_ACTIVE already set.
 	 */
-	where = xc_broadcast(0, (xcfunc_t)nullop, NULL, NULL);
-	xc_wait(where);
+	if (__predict_true(mp_online)) {
+		where = xc_broadcast(0, (xcfunc_t)nullop, NULL, NULL);
+		xc_wait(where);
+	}
 
 	for (;;) {
 		/* Collect flag values from each CPU. */
Index: subr_pserialize.c
===================================================================
RCS file: /cvsroot/src/sys/kern/subr_pserialize.c,v
retrieving revision 1.9
diff -u -p -r1.9 subr_pserialize.c
--- subr_pserialize.c	21 Nov 2017 08:49:14 -0000	1.9
+++ subr_pserialize.c	26 Dec 2017 07:47:57 -0000
@@ -157,6 +157,11 @@ pserialize_perform(pserialize_t psz)
 	KASSERT(psz->psz_owner == NULL);
 	KASSERT(ncpu > 0);
 
+	if (__predict_false(mp_online == false)) {
+		psz_ev_excl.ev_count++;
+		return;
+	}
+
 	/*
 	 * Set up the object and put it onto the queue.  The lock
 	 * activity here provides the necessary memory barrier to
Index: subr_psref.c
===================================================================
RCS file: /cvsroot/src/sys/kern/subr_psref.c,v
retrieving revision 1.9
diff -u -p -r1.9 subr_psref.c
--- subr_psref.c	14 Dec 2017 05:45:55 -0000	1.9
+++ subr_psref.c	26 Dec 2017 07:47:57 -0000
@@ -429,8 +429,14 @@ psreffed_p(struct psref_target *target,
 		.ret = false,
 	};
 
-	/* Ask all CPUs to say whether they hold a psref to the target.  */
-	xc_wait(xc_broadcast(0, &psreffed_p_xc, &P, NULL));
+	if (__predict_true(mp_online)) {
+		/*
+		 * Ask all CPUs to say whether they hold a psref to the
+		 * target.
+		 */
+		xc_wait(xc_broadcast(0, &psreffed_p_xc, &P, NULL));
+	} else
+		psreffed_p_xc(&P, NULL);
 
 	return P.ret;
 }
-----------------

 It might not be required to increment psz_ev_excl evcnt in softint_disestablish()
when mp_online == false.

--
-----------------------------------------------
                SAITOH Masanobu (msaitoh%execsw.org@localhost
                                 msaitoh%netbsd.org@localhost)