On Fri, 2017-02-03 at 14:37 +0100, Peter Zijlstra wrote: > On Fri, Feb 03, 2017 at 01:59:34PM +0100, Mike Galbraith wrote: > > FWIW, I'm not seeing stalls/hangs while beating hotplug up in tip. (so > > next grew a wart?) > > I've seen it on tip. It looks like hot unplug goes really slow when > there's running tasks on the CPU being taken down. > > What I did was something like: > > taskset -p $((1<<1)) $$ > for ((i=0; i<20; i++)) do while :; do :; done & done > > taskset -p $((1<<0)) $$ > echo 0 > /sys/devices/system/cpu/cpu1/online > > And with those 20 tasks stuck sucking cycles on CPU1, the unplug goes > _really_ slow and the RCU stall triggers. What I suspect happens is that > hotplug stops participating in the RCU state machine early, but only > tells RCU about it really late, and in between it gets suspicious it > takes too long. Ah. I wasn't doing a really hard pounding, just running a couple instances of Steven's script. To beat hell out of it, I add futextest, stockfish and a small kbuild on a big box. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
