Turn console printf buffering into a kernel option and only on

by default for sun4v where it is absolutely required.

This change moves the buffer from struct pcpu to the stack to avoid
using the critical section which created a LOR in a couple of cases
due to interaction with the tty code and kqueue. The LOR can't be
fixed with the critical section and the pcpu buffer can't be used
without the critical section.

Putting the buffer on the stack was my initial solution, but it was
pointed out that the stress on the stack might cause problems
depending on the call path. We don't have a way of creating tests
for those possible cases, so it's best to leave this as an option
for the time being. In time we may get enough data to enable this
option more generally.

1 files changed, 0 insertions, 5 deletions

diff --git a/sys/sys/pcpu.h b/sys/sys/pcpu.h
index fa54bc4..00a3cac 100644
--- a/sys/sys/pcpu.h
+++ b/sys/sys/pcpu.h
@@ -48,9 +48,6 @@
 struct pcb;
 struct thread;
 
-/* Size of the per-cpu console buffer for printf(). */
-#define	PCPU_CONS_BUFR	128
-
 /*
  * This structure maps out the global data that needs to be kept on a
  * per-cpu basis.  The members are accessed via the PCPU_GET/SET/PTR
@@ -74,8 +71,6 @@ struct pcpu {
 	int		pc_ktr_idx;		/* Index into trace table */
 	char		*pc_ktr_buf;
 #endif
-	char		pc_cons_bufr[PCPU_CONS_BUFR];
-						/* Console buffer */
 	PCPU_MD_FIELDS;
 	struct vmmeter	pc_cnt;			/* VM stats counters */
 	struct device	*pc_device;