2018-01-24 2:57 UTC+01:00, Frederic Weisbecker <frede...@kernel.org>: > On Tue, Jan 23, 2018 at 01:24:24PM -0500, David Miller wrote: >> From: Linus Torvalds <torva...@linux-foundation.org> >> Date: Tue, 23 Jan 2018 09:42:32 -0800 >> >> > But I wonder if the test triggers the "lets run lots of workqueue >> > threads", and then the single-threaded user space just gets blown out >> > of the water by many kernel threads. Each thread gets its own "fair" >> > amount of CPU, but.. >> >> If a single cpu's softirq deferral can end up running on multiple >> workqueue threads, indeed that's a serious problem. >> >> So if we're in a workqueue and it does a: >> >> schedule_work_on(this_cpu, currently_executing_work); >> >> it'll potentially make a new thread? >> >> That's exactly the code path that will get exercised during a UDP >> flood the way that vector_work_func() is implemented. > > It shouldn't create a new thread unless all other workers in the CPU > are voluntarily sleeping while executing a work. Also since softirqs > can't sleep, we shouldn't even have two vectors running concurrently > on workqueues. >
...unless I misunderstood workqueue internals or missed something, in which case we may try ordered workqueue.
