domains: Remove TPA sandbox domain for now

At the moment, the scheduler is wasting 50% of its time in an idle thread for
the application sandbox domain. Until we can figure out how to use these domains
more effectively, we'll reduce to a single domain.

Bug: 238811077
Change-Id: If40d01d5c94e31cc8d522dd5f906f857e363cc42
GitOrigin-RevId: 911f6fe046c61b8ce7e9ba00f8de0ec872997ec3

Author: jtg-google

apps/system/components/kata-os-common/src/scheduling/src/lib.rs

@@ -4,11 +4,14 @@
 
 /// Scheduling domains configured for seL4 TCBs.
 ///
-/// Currently we have this setup as a pair of domains, one for the system
-/// components and another for the third party application sandbox.
+/// Currently we have this setup as a single domain for all components, since we
+/// don't want to waste 50% of our time waiting for a mostly idle partition.
+///
+/// TODO: Figure out how to more effectively use these domains of execution, and
+/// how to prevent wasting time in an idle thread for a whole domain when no
+/// TCBs are scheduled there. See also b/238811077.
 ///
 #[derive(Debug, Eq, PartialEq, Copy, Clone)]
 pub enum Domain {
     System = 0,
-    AppSandbox,
 }

easy-settings.cmake

@@ -14,5 +14,5 @@ set(SIMULATION ON CACHE BOOL "Whether to build simulate script")
 set(RELEASE OFF CACHE BOOL "Performance optimized build")
 set(UseRiscVBBL OFF CACHE BOOL "Whether to use bbl")
 
-set(KernelNumDomains 2 CACHE STRING "How many scheduling domains to build for")
+set(KernelNumDomains 1 CACHE STRING "How many scheduling domains to build for")
 set(KernelDomainSchedule "${CMAKE_CURRENT_LIST_DIR}/kernel/round_robin_domain.c" CACHE INTERNAL "Domain scheduler algorithm")

kernel/round_robin_domain.c

@@ -13,10 +13,19 @@
  * other half. Note that even if there's nothing to run in the third-party
  * application domain, the scheduler will schedule an idle thread to ensure that
  * domain gets it's allocated share of time.
+ *
+ * TODO(jtgans,sleffler): Figure out how to better use these domains for
+ * scheduling applications. We don't really want to use a full 50% duty cycle
+ * for third party applications -- this wastes too much time. See also
+ * b/238811077.
+ *
+ * NOTE: Only a single domain is currently enabled, as per the commented section
+ * below. Any time the below schedule is changed, the number of domains
+ * configured in easy-settings.cmake must also be changed.
  */
 const dschedule_t ksDomSchedule[] = {
     {.domain = 0, .length = 1},  // System domain
-    {.domain = 1, .length = 1},  // Third party application domain
+    /*  {.domain = 1, .length = 1},  // Third party application domain */
 };
 
 const word_t ksDomScheduleLength = sizeof(ksDomSchedule) / sizeof(dschedule_t);