From 9b8eae7248dad42091204f83ed3448e661456af1 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Thu, 7 Feb 2008 00:13:37 -0800 Subject: Documentation: create new scheduler/ subdirectory The top-level Documentation/ directory is unmanageably large, so we should take any obvious opportunities to move stuff into subdirectories. These sched-*.txt files seem an obvious easy case. Signed-off-by: J. Bruce Fields Cc: Ingo Molnar Acked-by: Randy Dunlap Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/sched-domains.txt | 70 ----------------------------------------- 1 file changed, 70 deletions(-) delete mode 100644 Documentation/sched-domains.txt (limited to 'Documentation/sched-domains.txt') diff --git a/Documentation/sched-domains.txt b/Documentation/sched-domains.txt deleted file mode 100644 index a9e990ab980..00000000000 --- a/Documentation/sched-domains.txt +++ /dev/null @@ -1,70 +0,0 @@ -Each CPU has a "base" scheduling domain (struct sched_domain). These are -accessed via cpu_sched_domain(i) and this_sched_domain() macros. The domain -hierarchy is built from these base domains via the ->parent pointer. ->parent -MUST be NULL terminated, and domain structures should be per-CPU as they -are locklessly updated. - -Each scheduling domain spans a number of CPUs (stored in the ->span field). -A domain's span MUST be a superset of it child's span (this restriction could -be relaxed if the need arises), and a base domain for CPU i MUST span at least -i. The top domain for each CPU will generally span all CPUs in the system -although strictly it doesn't have to, but this could lead to a case where some -CPUs will never be given tasks to run unless the CPUs allowed mask is -explicitly set. A sched domain's span means "balance process load among these -CPUs". - -Each scheduling domain must have one or more CPU groups (struct sched_group) -which are organised as a circular one way linked list from the ->groups -pointer. The union of cpumasks of these groups MUST be the same as the -domain's span. The intersection of cpumasks from any two of these groups -MUST be the empty set. The group pointed to by the ->groups pointer MUST -contain the CPU to which the domain belongs. Groups may be shared among -CPUs as they contain read only data after they have been set up. - -Balancing within a sched domain occurs between groups. That is, each group -is treated as one entity. The load of a group is defined as the sum of the -load of each of its member CPUs, and only when the load of a group becomes -out of balance are tasks moved between groups. - -In kernel/sched.c, rebalance_tick is run periodically on each CPU. This -function takes its CPU's base sched domain and checks to see if has reached -its rebalance interval. If so, then it will run load_balance on that domain. -rebalance_tick then checks the parent sched_domain (if it exists), and the -parent of the parent and so forth. - -*** Implementing sched domains *** -The "base" domain will "span" the first level of the hierarchy. In the case -of SMT, you'll span all siblings of the physical CPU, with each group being -a single virtual CPU. - -In SMP, the parent of the base domain will span all physical CPUs in the -node. Each group being a single physical CPU. Then with NUMA, the parent -of the SMP domain will span the entire machine, with each group having the -cpumask of a node. Or, you could do multi-level NUMA or Opteron, for example, -might have just one domain covering its one NUMA level. - -The implementor should read comments in include/linux/sched.h: -struct sched_domain fields, SD_FLAG_*, SD_*_INIT to get an idea of -the specifics and what to tune. - -For SMT, the architecture must define CONFIG_SCHED_SMT and provide a -cpumask_t cpu_sibling_map[NR_CPUS], where cpu_sibling_map[i] is the mask of -all "i"'s siblings as well as "i" itself. - -Architectures may retain the regular override the default SD_*_INIT flags -while using the generic domain builder in kernel/sched.c if they wish to -retain the traditional SMT->SMP->NUMA topology (or some subset of that). This -can be done by #define'ing ARCH_HASH_SCHED_TUNE. - -Alternatively, the architecture may completely override the generic domain -builder by #define'ing ARCH_HASH_SCHED_DOMAIN, and exporting your -arch_init_sched_domains function. This function will attach domains to all -CPUs using cpu_attach_domain. - -Implementors should change the line -#undef SCHED_DOMAIN_DEBUG -to -#define SCHED_DOMAIN_DEBUG -in kernel/sched.c as this enables an error checking parse of the sched domains -which should catch most possible errors (described above). It also prints out -the domain structure in a visual format. -- cgit v1.2.3