On 2017-07-27 22:45:38 [+0000], Carol Wong wrote: > Hi, Hi, > On my test setup, cyclictest is reporting max latency > 500 us in 4.9.33-rt23 and 4.9.35-rt25. Max latency is small in 4.9.33-rt22 and 4.9.33-rt21 (< 50 us) under the same conditions. > > My test setup uses a Core i7 (3.4GHz 3rd gen) with hyper-threading disabled. The system is under heavy load (60-90% each core) servicing network traffic and performing arithmetic on the packet payloads. Interrupt rate is approximately 60K intr/s. I've tried a few different NICs (e1000, e1000e, and ixgbe) with the same result. Occasional big hits start occurring within 30 minutes. > > I tried a modified 4.9.33-rt23 kernel with the following commit removed: > <https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git/commit/kernel/sched/core.c?h=v4.9-rt&id=1dc89be37874bfc7bb4a0ea7c45492d7db39f62b> > The big latency hits do not happen with this commit backed out. so you say with this change is responsible for 450us of latency? This change should be a nop if you don't change the task's CPU-mask while the task is in a migrate-disable section. Do I miss something? Is part of your workload changing cpu-affinity mask? > I've not yet had a chance to try a 4.11 kernel, but it looks like there's been recent work on migrate_disable/enable in that branch. Maybe a backport to 4.9 is needed? v4.11 should have the same change you just pointed out. > Cheers, > Carol > Sebastian -- 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
