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CC-lock is based on flat-lock combining algorithm. In this lock, only one thread, called combiner thread the request of critical section. So, combiner thread can exploit locality and aviod high contetetion between lock varible. When each cpu use only one node, let's assume lock hold node A. In this case, node A's (wait, completed) status should be (false, false). Lock | A When A,B cpu race occured, Let's assume that B is win. Then, B will try to spin on A's wait Status. A -> B w:F w:T At the same time, A was enqueued. So, A's wait status was set to True like below. A -> B -> A w:T w:T w:T This lead to deadlock. To avoid above node-reusing problem, each cpu has two cc_node. Those node are used alternately. A_0 -> B_0 -> A_1 w:f w:T w:T Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Test reported that there is a deadlock. Situation are
below.
Node(0, 1) {
req = 00000000d0495726,
params = 000000002f36f5ac,
wait = 0, completed = 1,
refcount = 0,
Next (2, 0)
Prev (0, 0)
}
Node(2, 0) {
req = 00000000d0495726,
params = 000000002f36f5ac,
wait = 1, completed = 0,
refcount = 0,
Next (2, 1)
Prev (0, 1)
}
Node (0, 1)'s request are handled. So, it wait,
completed status are (0, 1). But, it's next node
Node(2, 0)'s wait are still 1. The combiner thread
should set Node(2, 0) wait = 0. Previous logic
set wait = 0, when DECODE_CPU(pending_cpu) != NR_CPUS.
But there can be race between combiner thread
and normal thread. In the combiner thread it
check node->req first, then it check node->next.
So there could be a situation below
Node(0, 1) Node(2, 0)
prev->req = req
if(pending->req)
...
DECODE_CPU(pending->next)
prev->next = this_cpu
To fix this, combiner thread check node->next first.
Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Previous, test thread used jiffes to measure the spent time. But, it's resolution is low. So all the results are zero or one. So use sched_clock. Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
To keep order of reading node->next and writing of node->wait, node->completed, smp_mb should be used instead of smp_mb(). So fix it Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Using the "echo 2 > trigger", spinlock based benchmark can be run. Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
This script provide measurement result parsing and plotting features.
To optmize, enable debug code when DEBUG is defined Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
To reduce inter-node traffic, add delay when it fail to get global lock. The time of delay is a value from experimental result. Signed-off-by: wonhyuk yang <vvghjk1234@gmail.com>
This reverts commit d4ee7b4.
Add new benchmark that measure the time of list operation.
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Revert highly contended benchmark. This patch is experimental feature.
Plus, Add list benchmark infrastructure.