Messages in this thread | | | Date | Thu, 06 Sep 2012 09:55:18 +0800 | From | Lai Jiangshan <> | Subject | Re: [PATCH 04/10 V4] workqueue: add manage_workers_slowpath() |
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On 09/05/2012 09:12 AM, Tejun Heo wrote: > Hello, Lai. > > On Sun, Sep 02, 2012 at 12:28:22AM +0800, Lai Jiangshan wrote: >> If hotplug code grabbed the manager_mutex and worker_thread try to create >> a worker, the manage_worker() will return false and worker_thread go to >> process work items. Now, on the CPU, all workers are processing work items, >> no idle_worker left/ready for managing. It breaks the concept of workqueue >> and it is bug. >> >> So when manage_worker() failed to grab the manager_mutex, it should >> try to enter normal process contex and then compete on the manager_mutex >> instead of return false. >> >> To safely do this, we add manage_workers_slowpath() and the worker >> go to process work items mode to do the managing jobs. thus >> managing jobs are processed via work item and can free to compete >> on manager_mutex. > > Ummm.... this seems overly complicated. How about scheduling rebind > work to a worker and forcing it to break out of the work processing > loop? I think it can be done fairly easily using POOL_MANAGE_WORKERS > - set it from the rebind function, break out of work processing loop > if it's set, replace need_to_manage_workers() with POOL_MANAGE_WORKERS > test (the function really isn't necessary) and always jump back to > recheck afterwards. It might need a bit more mangling here and there > but that should be the essence of it. I'll give a stab at it later > today. >
This approach is a little like my unsent approach3.(I will explain in other mail) This approach is most complicated and changing more code if it is implemented.
First we should rebind/unbind separated by pool. because, if we queue the rebind-work to high-pri pool, we will break normal-pool vice versa
and this forces us move DISASSOCIATED to pool-flags. and this forces us add more code in cpu-notify
second, reuse POOL_MANAGE_WORKERS, or add new one.
third, need to restruct of rebind/unbind and change a lot in worker_thread.
my partial/unsent approach3 has almost the same problem. (different, my approach3 don't use work item, it is checked and called from the "recheck" label of worker_thread. it is called with WORKER_PREP bit set and it uses "mutex_trylock" to grab lock like manage_workers())
how much code will be changed for only unbind part of this approach:
kernel/workqueue.c | 103 ++++++++++++++++++++++++++++++++++++++-------------- 1 files changed, 76 insertions(+), 27 deletions(-)
Thanks Lai
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