f91aa773be
wakeup_one() and underlying sleepq_signal() spend additional time trying to be fair, waking thread with highest priority, sleeping longest time. But in case of taskqueue there are many absolutely identical threads, and any fairness between them is quite pointless. It makes even worse, since round-robin wakeups not only make previous CPU affinity in scheduler quite useless, but also hide from user chance to see CPU bottlenecks, when sequential workload with one request at a time looks evenly distributed between multiple threads. This change adds new SLEEPQ_UNFAIR flag to sleepq_signal(), making it wakeup thread that went to sleep last, but no longer in context switch (to avoid immediate spinning on the thread lock). On top of that new wakeup_any() function is added, equivalent to wakeup_one(), but setting the flag. On top of that taskqueue(9) is switchied to wakeup_any() to wakeup its threads. As result, on 72-core Xeon v4 machine sequential ZFS write to 12 ZVOLs with 16KB block size spend 34% less time in wakeup_any() and descendants then it was spending in wakeup_one(), and total write throughput increased by ~10% with the same as before CPU usage. Reviewed by: markj, mmacy MFC after: 2 weeks Sponsored by: iXsystems, Inc. Differential Revision: https://reviews.freebsd.org/D20669 |
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