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Date: Thu, 26 Oct 2017 13:59:04 -0600 From: Jonathan Haws <hawsjr@...il.com> To: linux-kernel@...r.kernel.org Subject: POSIX Message Queue Priority Scheduling Can someone explain to me how message queues handle waking multiple threads blocked on a single message queue? My situation is I have multiple writers blocking on a full message queue, each posting messages with priority equal to the thread priority. I want to make sure they wake and post in priority order, however my application is behaving as if they are waking in FIFO order (i.e. the order in which they blocked). Each blocking thread is scheduled with the SCHED_FIFO policy with a different priority with system level scope. I've searched the Internet high and low for something describing how this should work and all I can find is POSIX man pages describing that multiple blockers wake in priority order **if Priority Scheduling is supported**. Since the kernel scheduler is a priority scheduler I would think that the threads would wake in priority order and post to the queue, however that doesn't appear to be the case. I'm sure I'm just missing some subtle detail and was hoping the experts here on this list can help shine some light on what I'm seeing, since its at the kernel level that these threads are made ready to run. I have a small test application that I can post here if necessary. If this isn't the right place to ask this, by all means let me know and direct me to the right forum. Thanks! Jon -- Jonathan R. Haws hawsjr@...il.com
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