Re: patch review: avoid com delay() in VMs

Emile `iMil' Heitor wrote:

> com_attach_subr() in sys/dev/ic/com.c has a delay(10000) waiting for
> output to finish, this is very unlikely to be useful inside a virtual
> machine and slows down boot time in such machine.
> I propose the following approach:

Expanding on Martin's suggestion, I wonder if something like this
is better (completely untested!)?  This way we'd always have
inside_vm_guest() available to remove the #ifdef check from any
consumers and reduce clutter a little bit.

diff --git a/sys/arch/x86/include/cpu.h b/sys/arch/x86/include/cpu.h
index 6c26dc624b1..94c99946bc9 100644
--- a/sys/arch/x86/include/cpu.h
+++ b/sys/arch/x86/include/cpu.h
@@ -558,6 +558,12 @@ vm_guest_is_pvh(void)
         }
  }

+#define __HAVE_VIRTUAL_HOST_P
+static __inline bool __unused
+inside_vm_guest(void)
+{
+       return vm_guest != VM_GUEST_NO;
+}
+
  /* cpu_topology.c */
  void   x86_cpu_topology(struct cpu_info *);
diff --git a/sys/dev/ic/com.c b/sys/dev/ic/com.c
index 539b6597accd..f835e493184c 100644
--- a/sys/dev/ic/com.c
+++ b/sys/dev/ic/com.c
@@ -589,8 +589,15 @@ com_attach_subr(struct com_softc *sc)
                        break;
                }

+               if (!inside_vm_guest()) {
+                       /*
+                        * Wait for output to finish.  No need for
+                        * a delay on virtual machines.
+                        */
+                       delay(10000);
+               }
+
                /* Make sure the console is always "hardwired". */
-               delay(10000);                   /* wait for output to finish */
                if (is_console) {
                        SET(sc->sc_hwflags, COM_HW_CONSOLE);
                }
diff --git a/sys/sys/cpu.h b/sys/sys/cpu.h
index 0393f9c0058a..3f8a0d1ea684 100644
--- a/sys/sys/cpu.h
+++ b/sys/sys/cpu.h
@@ -50,6 +50,14 @@ void cpu_idle(void);
 #endif
 #endif

+#ifndef __HAVE_VIRTUAL_HOST_P
+static __inline bool __unused
+inside_vm_guest(void)
+{
+       return 0;
+}
+#endif /* !__HAVE_VIRTUAL_HOST_P */
+
 #ifndef cpu_need_resched
 void cpu_need_resched(struct cpu_info *, struct lwp *, int);
 #endif

Cheers,
Simon.