Commit major SMP cleanups and move the BGL (big giant lock) in the

    syscall path inward.  A system call may select whether it needs the MP
    lock or not (the default being that it does need it).

    A great deal of conditional SMP code for various deadended experiments
    has been removed.  'cil' and 'cml' have been removed entirely, and the
    locking around the cpl has been removed.  The conditional
    separately-locked fast-interrupt code has been removed, meaning that
    interrupts must hold the CPL now (but they pretty much had to anyway).
    Another reason for doing this is that the original separate-lock for
    interrupts just doesn't apply to the interrupt thread mechanism being
    contemplated.

    Modifications to the cpl may now ONLY occur while holding the MP
    lock.  For example, if an otherwise MP safe syscall needs to mess with
    the cpl, it must hold the MP lock for the duration and must (as usual)
    save/restore the cpl in a nested fashion.

    This is precursor work for the real meat coming later: avoiding having
    to hold the MP lock for common syscalls and I/O's and interrupt threads.
    It is expected that the spl mechanisms and new interrupt threading
    mechanisms will be able to run in tandem, allowing a slow piecemeal
    transition to occur.

    This patch should result in a moderate performance improvement due to
    the considerable amount of code that has been removed from the critical
    path, especially the simplification of the spl*() calls.  The real
    performance gains will come later.

Approved by: jkh
Reviewed by: current, bde (exception.s)
Some work taken from: luoqi's patch

1 files changed, 21 insertions, 80 deletions

diff --git a/sys/i386/include/smptests.h b/sys/i386/include/smptests.h
index dd89728..f9ac4a3 100644
--- a/sys/i386/include/smptests.h
+++ b/sys/i386/include/smptests.h
@@ -63,65 +63,6 @@
 #define PUSHDOWN_LEVEL_3_NOT
 #define PUSHDOWN_LEVEL_4_NOT
 
-
-/*
- * XXX some temp debug control of cpl locks
- */
-#ifdef PUSHDOWN_LEVEL_2
-#define REAL_ECPL	/* exception.s:		SCPL_LOCK/SCPL_UNLOCK */
-#define REAL_ICPL	/* ipl.s:		CPL_LOCK/CPL_UNLOCK/FAST */
-#define REAL_AICPL	/* apic_ipl.s:		SCPL_LOCK/SCPL_UNLOCK */
-#define REAL_AVCPL	/* apic_vector.s:	CPL_LOCK/CPL_UNLOCK */
-#define REAL_IFCPL	/* ipl_funcs.c:		SCPL_LOCK/SCPL_UNLOCK */
-#endif /* PUSHDOWN_LEVEL_2 */
-
-/*
- * The xCPL_LOCK/xCPL_UNLOCK defines control the spinlocks
- * that protect cpl/cml/cil and the spl functions.
- */
-#ifdef REAL_ECPL
-#define ECPL_LOCK		SCPL_LOCK
-#define ECPL_UNLOCK		SCPL_UNLOCK
-#else
-#define ECPL_LOCK
-#define ECPL_UNLOCK
-#endif /* REAL_ECPL */
-
-#ifdef REAL_ICPL
-#define ICPL_LOCK		CPL_LOCK
-#define ICPL_UNLOCK		CPL_UNLOCK
-#define FAST_ICPL_UNLOCK	movl	$0, _cpl_lock
-#else
-#define ICPL_LOCK
-#define ICPL_UNLOCK
-#define FAST_ICPL_UNLOCK
-#endif /* REAL_ICPL */
-
-#ifdef REAL_AICPL
-#define AICPL_LOCK		SCPL_LOCK
-#define AICPL_UNLOCK		SCPL_UNLOCK
-#else
-#define AICPL_LOCK
-#define AICPL_UNLOCK
-#endif /* REAL_AICPL */
-
-#ifdef REAL_AVCPL
-#define AVCPL_LOCK		CPL_LOCK
-#define AVCPL_UNLOCK		CPL_UNLOCK
-#else
-#define AVCPL_LOCK
-#define AVCPL_UNLOCK
-#endif /* REAL_AVCPL */
-
-#ifdef REAL_IFCPL
-#define IFCPL_LOCK()		SCPL_LOCK()
-#define IFCPL_UNLOCK()		SCPL_UNLOCK()
-#else
-#define IFCPL_LOCK()
-#define IFCPL_UNLOCK()
-#endif /* REAL_IFCPL */
-
-
 /*
  * Debug version of simple_lock.  This will store the CPU id of the
  * holding CPU along with the lock.  When a CPU fails to get the lock
@@ -160,36 +101,40 @@
 
 
 /*
- * Regular INTerrupts without the giant lock, NOT READY YET!!!
+ * INTR_SIMPLELOCK has been removed, as the interrupt mechanism will likely
+ * not use this sort of optimization if we move to interrupt threads.
  */
 #ifdef PUSHDOWN_LEVEL_4
-#define INTR_SIMPLELOCK
 #endif
 
 
 /*
- * Separate the INTR() portion of cpl into another variable: cml.
+ * CPL_AND_CML has been removed.  Interrupt threads will eventually not
+ * use either mechanism so there is no point trying to optimize it.
  */
 #ifdef PUSHDOWN_LEVEL_3
-#define CPL_AND_CML
 #endif
 
 
 /*
- * Forces spl functions to spin while waiting for safe time to change cpl.
+ * SPL_DEBUG_POSTCODE/INTR_SPL/SPL_DEBUG - removed
  *
-#define SPL_DEBUG_POSTCODE	(slows the system down noticably)
+ * These functions were too expensive for the standard case but, more 
+ * importantly, we should be able to come up with a much cleaner way
+ * to handle the cpl.  Having to do any locking at all is a mistake
+ * for something that is modified as often as cpl is.
  */
-#ifdef PUSHDOWN_LEVEL_3
-#define INTR_SPL
-#define SPL_DEBUG
-#endif
-
 
 /*
+ * FAST_WITHOUTCPL - now made the default (define removed).  Text below 
+ * contains the current discussion.  I am confident we can find a solution
+ * that does not require us to process softints from a hard int, which can
+ * kill serial performance due to the lack of true hardware ipl's.
+ *
+ ****
+ *
  * Ignore the ipending bits when exiting FAST_INTR() routines.
  *
- ***
  * according to Bruce:
  *
  * setsoft*() may set ipending.  setsofttty() is actually used in the
@@ -209,21 +154,17 @@
  *  I finish making spl/cpl MP-safe.
  */
 #ifdef PUSHDOWN_LEVEL_1
-#define FAST_WITHOUTCPL
 #endif
 
 
 /*
- * Use a simplelock to serialize FAST_INTR()s.
- * sio.c, and probably other FAST_INTR() drivers, never expected several CPUs
- * to be inside them at once.  Things such as global vars prevent more
- * than 1 thread of execution from existing at once, so we serialize
- * the access of FAST_INTR()s via a simple lock.
- * One optimization on this would be a simple lock per DRIVER, but I'm
- * not sure how to organize that yet...
+ * FAST_SIMPLELOCK no longer exists, because it doesn't help us.  The cpu
+ * is likely to already hold the MP lock and recursive MP locks are now
+ * very cheap, so we do not need this optimization.  Eventually *ALL* 
+ * interrupts will run in their own thread, so there is no sense complicating
+ * matters now.
  */
 #ifdef PUSHDOWN_LEVEL_1
-#define FAST_SIMPLELOCK
 #endif