On 11/24/2021 7:24 PM, Tudor Cornea wrote:
The Kni kthreads seem to be re-scheduled at a granularity of roughly 1 millisecond right now, which seems to be insufficient for performing tests involving a lot of control plane traffic.Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it seems that the existing code cannot reschedule at the desired granularily, due to precision constraints of schedule_timeout_interruptible(). In our use case, we leverage the Linux Kernel for control plane, and it is not uncommon to have 60K - 100K pps for some signaling protocols. Since we are not in atomic context, the usleep_range() function seems to be more appropriate for being able to introduce smaller controlled delays, in the range of 5-10 microseconds. Upon reading the existing code, it would seem that this was the original intent. Adding sub-millisecond delays, seems unfeasible with a call to schedule_timeout_interruptible(). KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */ schedule_timeout_interruptible( usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL)); Below, we attempted a brief comparison between the existing implementation, which uses schedule_timeout_interruptible() and usleep_range(). We attempt to measure the CPU usage, and RTT between two Kni interfaces, which are created on top of vmxnet3 adapters, connected by a vSwitch. insmod rte_kni.ko kthread_mode=single carrier=on schedule_timeout_interruptible(usecs_to_jiffies(5)) kni_single CPU Usage: 2-4 % [root@localhost ~]# ping 1.1.1.2 -I eth1 PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data. 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms usleep_range(5, 10) kni_single CPU usage: 50% 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms usleep_range(20, 50) kni_single CPU usage: 24% 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms usleep_range(50, 100) kni_single CPU usage: 13% 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms usleep_range(100, 200) kni_single CPU usage: 7% 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms usleep_range(1000, 1100) kni_single CPU usage: 2% 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms Upon testing, usleep_range(1000, 1100) seems roughly equivalent in latency and cpu usage to the variant with schedule_timeout_interruptible(), while usleep_range(100, 200) seems to give a decent tradeoff between latency and cpu usage, while allowing users to tweak the limits for improved precision if they have such use cases. Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a softlockup on my kernel. Kernel panic - not syncing: softlockup: hung tasks CPU: 0 PID: 1226 Comm: kni_single Tainted: G W O 3.10 #1 <IRQ> [<ffffffff814f84de>] dump_stack+0x19/0x1b [<ffffffff814f7891>] panic+0xcd/0x1e0 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80 This patch also attempts to remove this option. References: [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt Signed-off-by: Tudor Cornea <[email protected]> --- v4: * Removed RTE_KNI_PREEMPT_DEFAULT configuration option v3: * Fixed unwrapped commit description warning * Changed from hrtimers to Linux High Precision Timers in docs * Added two tabs at the beginning of the new params description. Stephen correctly pointed out that the descriptions of the parameters for the Kni module are nonstandard w.r.t existing kernel code. I was thinking to preserve compatibility with the existing parameters of the Kni module for the moment, while an additional clean-up patch could format the descriptions to be closer to the kernel standard. v2: * Fixed some spelling errors
Reviewed-by: Ferruh Yigit <[email protected]> Only it doesn't apply cleanly because of the latest changes in the kni, can you please rebase it? Please keep the review tag in the new version after rebase.
