But if you're willing to accept that the people around you might just be idiots, and not actively planning your overthrow, then the pamphlet is a short and surprisingly amusing read. You can see the whole thing at https://www.cia.gov/news-information/featured-story-archive/2012-featured-story-archive/simple-sabotage.html .
Sending a message seems to do nothing (doesn't show up on the screen) for a good minute too.
"After a long struggle trying to figure out how to upload my pix to Google Photos or Google Plus and a final rejection when they said they didn't recognize the pix as images I gave up and went with Flickr, instead. The process was easy even for a IT phobe like me. What the heck is wrong with Google that they can't figure out photos???"
As part of rolling out Mesos/Aurora at TellApart we turned on cgroup CPU throttling. We're using the default cpu.cfs_period_us=100ms right now and have noticed that it really bumps up the variability of our 50th and 90th percentile latencies (interestingly, 99th and 99.9th don't move - probably because other factors dominate that far out). Clearly we're burning through the CPU early in the 100ms block and the whole application pauses for 60-80ms.
Note that because of online ad-bidding rules our applications have to respond within 30-40ms, otherwise the entire request is invalid. So I'm very willing to trade throughput for latency. 10-20% CPU overhead would probably pay for itself :)
I figured we have 3 levers to pull (assuming CPU/request cannot be fixed):
1. CPU/task (inversely proportional to # tasks of course). Adding more CPU basically "smears" the high-CPU events (a big request, GC, etc) and lowers the probability that throttling will occur.
2. Lower the # of threads. If have 3 CPU allocated then "ideally" we should never have more than 3 threads running so we don't get throttled. Work should queue up waiting on the thread (instead of pausing the entire app). In reality, controlling threads like this is difficult...
3. Lower the cpu.cfs_period_us setting (maybe 20ms?). That would make a much lower "max pause time". Combine this with "throwing away" requests that have expired (e.g. if the throttling kicked in) would probably eliminate a lot of the variability.
4. Turn off CPU enforcement altogether.
What have people tried? Especially curious what Borg did; I never looked into the kernel settings of LOW_LATENCY-class applications. Reading the Borg paper (http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/43438.pdf) it looks like (3) was dynamically changed, and perhaps (4) was true for most machines/tasks but also dynamically changed?
since you've run very low-latency stuff in cgroups...
- UC BerkeleyB.A. Mathematics, 2000 - 2002
- Fallout Shelter
- Twitter Inc.Staff Software Engineer, 2015 - present
- Software Engineer, 2005 - 2014
- TellApartSoftware Engineer, 2014 - 2015
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