On 2023-11-21 10:52, Peter Zijlstra wrote:
On Tue, Nov 21, 2023 at 03:46:43PM +0100, Peter Zijlstra wrote:
Why is this such a hard question?
Anyway, recapping from IRC:
preemptible, SRCU:
counter-array based, GP advances by increasing array index
and waiting for previous index to drop to 0.
notably, a GP can pass while a task is preempted but not within a
critical section.
SRCU has smp_mb() in the critical sections to improve GP.
Also:
preemptible only allows blocking when priority inheritance is
guarantees, which excludes doing I/O, and thus page faults.
Otherwise a long I/O could cause the system to OOM.
SRCU allows all kind of blocking, as long as the entire SRCU
domain does not mind waiting for a while before readers complete.
tasks:
waits for every task to pass schedule()
ensures that any pieces of text rendered unreachable before, is
actually unused after.
tasks-rude:
like tasks, but different? build to handle tracing while rcu-idle,
even though that was already deemed bad?
tasks-tracing-rcu:
extention of tasks to have critical-sections ? Should this simply be
tasks?
tasks-trace-rcu is meant to allow tasks to block/take a page fault
within the read-side. It is specialized for tracing and has a single
domain. It does not need the smp_mb on the read-side, which makes it
lower-overhead than SRCU.
Thanks,
Mathieu
Can someone complete, please?
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
