Vernon Mauery <vernux@xxxxxxxxxx> writes: > > So while this issue really hits -rt kernels hard, it has a real effect on > mainline kernels as well. The contention of the spinlocks is amplified > when they get turned into rt-mutexes, which causes a double context switch. The new adaptive spin heuristics that have been discussed some time ago didn't help? Unsurprisingly making locks a lot more expensive has drawbacks as you discovered. > &list->lock#3: 24517307 24643791 0.71 1286.62 56516392.42 34834296 44904018 0.60 164.79 31314786.02 > ------------- > &list->lock#3 15596927 [<ffffffff812474da>] dev_queue_xmit+0x2ea/0x468 The real "fix" would be probably to use a multi queue capable NIC and a NIC driver that sets up multiple queues for TX (normally they only do for RX). Then cores or a set of cores (often the number of cores is larger than the number of NIC queues) could avoid this problem. Disadvantage: more memory use. But then again I'm not sure it's worth it if the problem only happens in out of tree RT. -Andi -- ak@xxxxxxxxxxxxxxx -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
