xen: credit2: improve comments' style and definition of CSFLAG-s

Most of the comments describing the meaning of the
vCPU flags used by the scheduler miss the 'wings' (or
have other minor style issues).

Also, use 1U (instead of 1) as the base of shiftings.

No functional change intended.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 920a7cef950959c8b42265d4d7b515e600766c7a..b4829908ebdee471d4004aaaaa04020e1cb0d1af 100644 (file)
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -129,35 +129,47 @@
 /*
  * Basic constants
  */
-/* Default weight: How much a new domain starts with */
+/* Default weight: How much a new domain starts with. */
 #define CSCHED2_DEFAULT_WEIGHT       256
-/* Min timer: Minimum length a timer will be set, to
- * achieve efficiency */
+/*
+ * Min timer: Minimum length a timer will be set, to
+ * achieve efficiency.
+ */
 #define CSCHED2_MIN_TIMER            MICROSECS(500)
-/* Amount of credit VMs begin with, and are reset to.
+/*
+ * Amount of credit VMs begin with, and are reset to.
  * ATM, set so that highest-weight VMs can only run for 10ms
- * before a reset event. */
+ * before a reset event.
+ */
 #define CSCHED2_CREDIT_INIT          MILLISECS(10)
-/* Carryover: How much "extra" credit may be carried over after
- * a reset. */
+/*
+ * Amount of credit the idle vcpus have. It never changes, as idle
+ * vcpus does not consume credits, and it must be lower than whatever
+ * amount of credit 'regular' vcpu would end up with.
+ */
+#define CSCHED2_IDLE_CREDIT          (-(1U<<30))
+/*
+ * Carryover: How much "extra" credit may be carried over after
+ * a reset.
+ */
 #define CSCHED2_CARRYOVER_MAX        CSCHED2_MIN_TIMER
-/* Stickiness: Cross-L2 migration resistance.  Should be less than
- * MIN_TIMER. */
+/*
+ * Stickiness: Cross-L2 migration resistance.  Should be less than
+ * MIN_TIMER.
+ */
 #define CSCHED2_MIGRATE_RESIST       ((opt_migrate_resist)*MICROSECS(1))
-/* How much to "compensate" a vcpu for L2 migration */
+/* How much to "compensate" a vcpu for L2 migration. */
 #define CSCHED2_MIGRATE_COMPENSATION MICROSECS(50)
 /* Reset: Value below which credit will be reset. */
 #define CSCHED2_CREDIT_RESET         0
 /* Max timer: Maximum time a guest can be run for. */
 #define CSCHED2_MAX_TIMER            CSCHED2_CREDIT_INIT
 
-
-#define CSCHED2_IDLE_CREDIT                 (-(1<<30))
-
 /*
  * Flags
  */
-/* CSFLAG_scheduled: Is this vcpu either running on, or context-switching off,
+/*
+ * CSFLAG_scheduled: Is this vcpu either running on, or context-switching off,
  * a physical cpu?
  * + Accessed only with runqueue lock held
  * + Set when chosen as next in csched2_schedule().
@@ -167,8 +179,9 @@
  * + Checked to be false in runq_insert.
  */
 #define __CSFLAG_scheduled 1
-#define CSFLAG_scheduled (1<<__CSFLAG_scheduled)
-/* CSFLAG_delayed_runq_add: Do we need to add this to the runqueue once it'd done
+#define CSFLAG_scheduled (1U<<__CSFLAG_scheduled)
+/*
+ * CSFLAG_delayed_runq_add: Do we need to add this to the runqueue once it'd done
  * being context switched out?
  * + Set when scheduling out in csched2_schedule() if prev is runnable
  * + Set in csched2_vcpu_wake if it finds CSFLAG_scheduled set
@@ -176,20 +189,21 @@
  *   clears the bit.
  */
 #define __CSFLAG_delayed_runq_add 2
-#define CSFLAG_delayed_runq_add (1<<__CSFLAG_delayed_runq_add)
-/* CSFLAG_runq_migrate_request: This vcpu is being migrated as a result of a
+#define CSFLAG_delayed_runq_add (1U<<__CSFLAG_delayed_runq_add)
+/*
+ * CSFLAG_runq_migrate_request: This vcpu is being migrated as a result of a
  * credit2-initiated runq migrate request; migrate it to the runqueue indicated
  * in the svc struct. 
  */
 #define __CSFLAG_runq_migrate_request 3
-#define CSFLAG_runq_migrate_request (1<<__CSFLAG_runq_migrate_request)
+#define CSFLAG_runq_migrate_request (1U<<__CSFLAG_runq_migrate_request)
 /*
  * CSFLAG_vcpu_yield: this vcpu was running, and has called vcpu_yield(). The
  * scheduler is invoked to see if we can give the cpu to someone else, and
  * get back to the yielding vcpu in a while.
  */
 #define __CSFLAG_vcpu_yield 4
-#define CSFLAG_vcpu_yield (1<<__CSFLAG_vcpu_yield)
+#define CSFLAG_vcpu_yield (1U<<__CSFLAG_vcpu_yield)
 
 static unsigned int __read_mostly opt_migrate_resist = 500;
 integer_param("sched_credit2_migrate_resist", opt_migrate_resist);