On 11/28, Peter Zijlstra wrote: > > On Thu, Nov 28, 2013 at 02:31:52PM +0100, Oleg Nesterov wrote: > > On 11/28, Peter Zijlstra wrote: > > > > > > On Thu, Nov 28, 2013 at 12:45:42PM +0100, Oleg Nesterov wrote: > > > > It has? khelper is a workqueue thread, this flag is set by > > > > create_worker(). > > > > > > > > And it does kernel_thread() (not kthread_create()) so the child gets > > > > this > > > > flag too. > > > > > > Urgh, but that's still completely wrong. khelper is a singlethread > > > workqueue, those should be unbound and therefore should not have this > > > flag set at all. > > > > Well. This is debatable, but I leave this to you and Tejun ;) > > How can that be debatable? I don't see a single argument in favour of > doing that; its plain ridiculous.
Let me repeat, I do not pretend I understand the current implementation in details. However, I'd like to say that I do not think think this is ridiculous. I think this is clever. > > > In fact, I know people want to set affinity on khelper > > > > This is not that simple. Note that khelper itself is the rescuer thread, > > it doesn't not process the works. There are other kworker/u* threads which > > run the work queued on khelper_wq. There is a pool of threads. > > That's just fucked. WTF does singlethreaded mean then? Yes, the naming is misleading. But it was always misleading. "singlethreaded" meant a single thread, yes, but this just reflected the implementation details. What it actually meant is: not bound to any cpu, and the works can't race with each other. create_singlethread_workqueue() still has the same semantics due to WQ_UNBOUND && max_active == 1. So in this sense (max_active == 1) it is still single threaded, just (iiuc, Tejun can correct me) it does not guarantee that the kernel thread which actually runs the work will be always the same. > A single parent process for all usermode helpers makes so much sense; This was never true, at least in UMH_WAIT_PROC case. > not doing it is just weird. Why? Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
