Commits on Dec 21, 2023

1. spa: make read/write queues configurable …

   We are finding that as customers get larger and faster machines
   (hundreds of cores, large NVMe-backed pools) they keep hitting
   relatively low performance ceilings. Our profiling work almost always
   finds that they're running into bottlenecks on the SPA IO taskqs.
   Unfortunately there's often little we can advise at that point, because
   there's very few ways to change behaviour without patching.
   
   This commit adds two load-time parameters `zio_taskq_read` and
   `zio_taskq_write` that can configure the READ and WRITE IO taskqs
   directly.
   
   This achieves two goals: it gives operators (and those that support
   them) a way to tune things without requiring a custom build of OpenZFS,
   which is often not possible, and it lets us easily try different config
   variations in a variety of environments to inform the development of
   better defaults for these kind of systems.
   
   Because tuning the IO taskqs really requires a fairly deep understanding
   of how IO in ZFS works, and generally isn't needed without a pretty
   serious workload and an ability to identify bottlenecks, only minimal
   documentation is provided. Its expected that anyone using this is going
   to have the source code there as well.
   
   Signed-off-by: Rob Norris <[email protected]>
   Sponsored-by: Klara, Inc.
   Sponsored-by: Wasabi Technology, Inc.

   

   robn committed Dec 21, 2023
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