sched, doc: Beef up load balancing description
PATCH 1/1 sched, doc: Beef up load balancing description
Correct all function names pertaining to load balancing and explain shortly how load balancing is performed.
Signed-off-by Borislav Petkov <[email protected]>
--- Documentation/scheduler/sched-domains.txt | 32 ++++++++++++++++++++-------- 1 files changed, 23 insertions(+), 9 deletions(-)
Documentation/scheduler/sched-domains.txt +23 -9
@@ -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
Signature · 1 line
1.7.4.1.48.g5673d
Commit-ID: e2495b577324938f0209b4f895c5f205c7e47854 Gitweb: http://git.kernel.org/tip/e2495b577324938f0209b4f895c5f205c7e47854 Author: Borislav Petkov <[email protected]> AuthorDate: Sun, 27 Mar 2011 17:57:13 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 31 Mar 2011 13:00:35 +0200
sched, doc: Beef up load balancing description
Correct all function names pertaining to load balancing and explain shortly how load balancing is performed.
Signed-off-by Borislav Petkov <[email protected]>
Signed-off-by Peter Zijlstra <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by Ingo Molnar <[email protected]>
--- Documentation/scheduler/sched-domains.txt | 32 ++++++++++++++++++++-------- 1 files changed, 23 insertions(+), 9 deletions(-)
Documentation/scheduler/sched-domains.txt +23 -9
@@ -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