x86/uv: Work around UV2 BAU hangs

On SGI's UV2 the BAU (Broadcast Assist Unit) driver can hang
under a heavy load. To cure this:

- Disable the UV2 extended status mode (see UV2_EXT_SHFT), as
  this mode changes BAU behavior in more ways then just delivering
  an extra bit of status.  Revert status to just two meaningful bits,
  like UV1.

- Use no IPI-style resets on UV2.  Just give up the request for
  whatever the reason it failed and let it be accomplished with
  the legacy IPI method.

- Use no alternate sending descriptor (the former UV2 workaround
  bcp->using_desc and handle_uv2_busy() stuff).  Just disable the
  use of the BAU for a period of time in favor of the legacy IPI
  method when the h/w bug leaves a descriptor busy.

  -- new tunable: giveup_limit determines the threshold at which a hub is
     so plugged that it should do all requests with the legacy IPI method for a
     period of time
  -- generalize disable_for_congestion() (renamed disable_for_period()) for
     use whenever a hub should avoid using the BAU for a period of time

Also:

 - Fix find_another_by_swack(), which is part of the UV2 bug workaround

 - Correct and clarify the statistics (new stats s_overipilimit, s_giveuplimit,
   s_enters, s_ipifordisabled, s_plugged, s_congested)

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Link: http://lkml.kernel.org/r/20120622131459.GC31884@sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 18 insertions, 10 deletions

diff --git a/arch/x86/include/asm/uv/uv_bau.h b/arch/x86/include/asm/uv/uv_bau.h
index 847c00b..a06983c 100644
--- a/arch/x86/include/asm/uv/uv_bau.h
+++ b/arch/x86/include/asm/uv/uv_bau.h
@@ -140,6 +140,9 @@
 #define IPI_RESET_LIMIT			1
 /* after this # consecutive successes, bump up the throttle if it was lowered */
 #define COMPLETE_THRESHOLD		5
+/* after this # of giveups (fall back to kernel IPI's) disable the use of
+   the BAU for a period of time */
+#define GIVEUP_LIMIT			100
 
 #define UV_LB_SUBNODEID			0x10
 
@@ -166,7 +169,6 @@
 #define FLUSH_RETRY_TIMEOUT		2
 #define FLUSH_GIVEUP			3
 #define FLUSH_COMPLETE			4
-#define FLUSH_RETRY_BUSYBUG		5
 
 /*
  * tuning the action when the numalink network is extremely delayed
@@ -175,7 +177,7 @@
 						   microseconds */
 #define CONGESTED_REPS			10	/* long delays averaged over
 						   this many broadcasts */
-#define CONGESTED_PERIOD		30	/* time for the bau to be
+#define DISABLED_PERIOD			10	/* time for the bau to be
 						   disabled, in seconds */
 /* see msg_type: */
 #define MSG_NOOP			0
@@ -520,7 +522,12 @@ struct ptc_stats {
 	unsigned long	s_uv2_wars;		/* uv2 workaround, perm. busy */
 	unsigned long	s_uv2_wars_hw;		/* uv2 workaround, hiwater */
 	unsigned long	s_uv2_war_waits;	/* uv2 workaround, long waits */
-	unsigned long   s_enters;		/* entries to the driver */
+	unsigned long	s_overipilimit;		/* over the ipi reset limit */
+	unsigned long	s_giveuplimit;		/* disables, over giveup limit*/
+	unsigned long	s_enters;		/* entries to the driver */
+	unsigned long	s_ipifordisabled;	/* fall back to IPI; disabled */
+	unsigned long	s_plugged;		/* plugged by h/w bug*/
+	unsigned long	s_congested;		/* giveup on long wait */
 	/* destination statistics */
 	unsigned long	d_alltlb;		/* times all tlb's on this
 						   cpu were flushed */
@@ -588,8 +595,7 @@ struct bau_control {
 	int			ipi_attempts;
 	int			conseccompletes;
 	short			nobau;
-	int			baudisabled;
-	int			set_bau_off;
+	short			baudisabled;
 	short			cpu;
 	short			osnode;
 	short			uvhub_cpu;
@@ -598,14 +604,16 @@ struct bau_control {
 	short			cpus_in_socket;
 	short			cpus_in_uvhub;
 	short			partition_base_pnode;
-	short			using_desc; /* an index, like uvhub_cpu */
-	unsigned int		inuse_map;
+	short			busy;       /* all were busy (war) */
 	unsigned short		message_number;
 	unsigned short		uvhub_quiesce;
 	short			socket_acknowledge_count[DEST_Q_SIZE];
 	cycles_t		send_message;
+	cycles_t		period_end;
+	cycles_t		period_time;
 	spinlock_t		uvhub_lock;
 	spinlock_t		queue_lock;
+	spinlock_t		disable_lock;
 	/* tunables */
 	int			max_concurr;
 	int			max_concurr_const;
@@ -616,9 +624,9 @@ struct bau_control {
 	int			complete_threshold;
 	int			cong_response_us;
 	int			cong_reps;
-	int			cong_period;
-	unsigned long		clocks_per_100_usec;
-	cycles_t		period_time;
+	cycles_t		disabled_period;
+	int			period_giveups;
+	int			giveup_limit;
 	long			period_requests;
 	struct hub_and_pnode	*thp;
 };