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author | David S. Miller <davem@davemloft.net> | 2011-04-11 20:44:25 (GMT) |
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committer | David S. Miller <davem@davemloft.net> | 2011-04-11 20:44:25 (GMT) |
commit | 1c01a80cfec6f806246f31ff2680cd3639b30e67 (patch) | |
tree | 0b554aad2ec1da71ecf6339d4ba51617bfe1dc3c /Documentation/scheduler/sched-domains.txt | |
parent | c44d79950b2daa1025e62eede73e4e4a274d1ef3 (diff) | |
parent | 4a9f65f6304a00f6473e83b19c1e83caa1e42530 (diff) | |
download | linux-fsl-qoriq-1c01a80cfec6f806246f31ff2680cd3639b30e67.tar.xz |
Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
Conflicts:
drivers/net/smsc911x.c
Diffstat (limited to 'Documentation/scheduler/sched-domains.txt')
-rw-r--r-- | Documentation/scheduler/sched-domains.txt | 32 |
1 files changed, 23 insertions, 9 deletions
diff --git a/Documentation/scheduler/sched-domains.txt b/Documentation/scheduler/sched-domains.txt index 373ceac..b7ee379 100644 --- a/Documentation/scheduler/sched-domains.txt +++ b/Documentation/scheduler/sched-domains.txt @@ -1,8 +1,7 @@ -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 +Each CPU has a "base" scheduling domain (struct sched_domain). 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. +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 @@ -26,11 +25,26 @@ 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. +In kernel/sched.c, trigger_load_balance() is run periodically on each CPU +through scheduler_tick(). It raises a softirq after the next regularly scheduled +rebalancing event for the current runqueue has arrived. The actual load +balancing workhorse, run_rebalance_domains()->rebalance_domains(), is then run +in softirq context (SCHED_SOFTIRQ). + +The latter function takes two arguments: the current CPU and whether it was idle +at the time the scheduler_tick() happened and iterates over all sched domains +our CPU is on, starting from its base domain and going up the ->parent chain. +While doing that, it checks to see if the current domain has exhausted its +rebalance interval. If so, it runs load_balance() on that domain. It then checks +the parent sched_domain (if it exists), and the parent of the parent and so +forth. + +Initially, load_balance() finds the busiest group in the current sched domain. +If it succeeds, it looks for the busiest runqueue of all the CPUs' runqueues in +that group. If it manages to find such a runqueue, it locks both our initial +CPU's runqueue and the newly found busiest one and starts moving tasks from it +to our runqueue. The exact number of tasks amounts to an imbalance previously +computed while iterating over this sched domain's groups. *** Implementing sched domains *** The "base" domain will "span" the first level of the hierarchy. In the case |