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ZIL introduced dependencies between its write ZIOs to permit flush defer, when we flush vdev caches only once all the write ZIOs has completed. But it was recently spotted that it serializes not only ZIO completions handling, but also their ready stage. It means ZIO pipeline can't calculate checksums for the following ZIOs until all the previous are checksumed, even though it is not required. On a systems where memory throughput of a single CPU core is limited, it creates single-core CPU bottleneck, which is difficult to see due to ZIO pipeline design with many taskqueue threads. While it would be great to bypass the ready stage waits, it would require changes to ZIO code, and I haven't found a clean way to do it. But I've noticed that we don't need any dependency between the write ZIOs if the previous one has some waiters, which means it won't defer any flushes and work as a barrier for the earlier ones. Bypassing it won't help large single-thread writes, since all the write ZIOs except the last in that case won't have waiters, and so will be dependent. But in that case the ZIO processing might not be a bottleneck, since there will be only one thread populating the write buffers, that will likely be the bottleneck. But bypassing the ZIO dependency on multi-threaded write workloads really allows them to scale beyond the checksuming throughput of one CPU core. My tests with writing 12 files on a same dataset on a pool with 4 striped NVMes as SLOGs from 12 threads with 1MB blocks on a system with Xeon Silver 4114 CPU show total throughput increase from 4.3GB/s to 8.5GB/s, increasing the SLOGs busy from ~30% to ~70%. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Rob Norris <robn@despairlabs.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes #17458 |
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 13.0-RELEASE.