Merge pull request #6 from metaspace/null

null_blk: Add description and benchmark results

Author: ojeda

SUMMARY.md

@@ -22,6 +22,7 @@
 ## Users
 
   - [NVMe Driver](NVMe-driver.md)
+  - [Null Block Driver](Null-Block-Driver.md)
   - [Android Binder Driver](Android-Binder-Driver.md)
 
 # Links

src/Null-Block-Driver.md

@@ -0,0 +1,91 @@
+
+# Null Block Driver
+
+The Rust null block driver `rnull` is an effort to implement a drop in
+replacement for `null_blk` in Rust.
+
+A null block driver is a good opportunity to evaluate Rust bindings for the
+block layer. It is a small and simple driver and thus should be simple to reason
+about. Further, the null block driver is not usually deployed in production
+environments. Thus, it should be fairly straight forward to review, and any
+potential issues are not going to bring down any production workloads.
+
+Being small and simple, the null block driver is a good place to introduce the
+Linux kernel storage community to Rust. This will help prepare the community for
+future Rust projects and facilitate a better maintenance process for these
+projects.
+
+[Statistics](https://lore.kernel.org/all/[email protected]/) from the
+commit log of the [C `null_blk`
+driver](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/drivers/block/null_blk?h=v6.1)
+([before
+move](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/drivers/block/null_blk_main.c?h=v6.1&id=ea17fd354ca8afd3e8962a77236b1a9a59262fdd))
+show that the C null block driver has had a significant amount of memory safety
+related problems in the past. 41% of fixes merged for the C null block driver
+are fixes for memory safety issues. This makes the null block driver a good
+candidate for rewriting in Rust.
+
+The driver is implemented entirely in safe Rust, with all unsafe code fully
+contained in the abstractions that wrap the C APIs.
+
+## Features
+
+Implemented features:
+
+ - `blk-mq` support
+ - Direct completion of IO
+ - Read and write requests
+ - Optional memory backing
+
+Features available in the C `null_blk` driver that are currently not implemented
+in this work:
+
+ - Bio-based submission
+ - NUMA support
+ - Block size configuration
+ - Multiple devices
+ - Dynamic device creation/destruction
+ - Soft-IRQ and timer mode
+ - Queue depth configuration
+ - Queue count configuration
+ - Discard operation support
+ - Cache emulation
+ - Bandwidth throttling
+ - Per node hctx
+ - IO scheduler configuration
+ - Blocking submission mode
+ - Shared tags configuration (for >1 device)
+ - Zoned storage support
+ - Bad block simulation
+ - Poll queues
+
+## Resources
+
+ - [Patches for 6.6](https://github.com/metaspace/linux/tree/null_blk-next-for-6.6)
+ - [Original RFC Patches](https://github.com/metaspace/linux/tree/null_block-RFC)
+ - [Mailing List Post](https://lore.kernel.org/all/[email protected]/)
+
+# Performance
+
+## Setup
+
+ - 12th Gen Intel(R) Core(TM) i5-12600
+ - 32 GB DRAM
+ - 1x INTEL MEMPEK1W016GA (PCIe 3.0 x2)
+ - Debian Bullseye userspace
+
+## Results
+
+In most cases there is less than 2% difference between the Rust and C drivers.
+
+![](./rnull/read-iops.svg)
+![](./rnull/write-iops.svg)
+![](./rnull/randread-iops.svg)
+![](./rnull/randwrite-iops.svg)
+![](./rnull/readwrite-iops.svg)
+![](./rnull/randrw-iops.svg)
+
+# Contact
+
+Please contact Andreas Hindborg through
+[Zulip](Contact.md#zulip-chat).