mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-24 21:10:51 +07:00
e29c98d12b
SCHED_DOMAIN_DEBUG mentioned in the Documentation for sched-domains for enabling sched-domains debugging doesn't exist anymore. Update the documentation to reflect the correct way of enabling sched-domain debugging. Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
68 lines
3.6 KiB
Plaintext
68 lines
3.6 KiB
Plaintext
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.
|
|
|
|
The sched-domains debugging infrastructure can be enabled by enabling
|
|
CONFIG_SCHED_DEBUG. 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.
|