Re: [RFC PATCH 00/11] Rust null block driver

["Andreas Hindborg (Samsung)" <nmi@metaspace.dk>]

Hi,

Yexuan Yang <1182282462@bupt.edu.cn> writes:

>> Over the 432 benchmark configurations, the relative performance of the Rust
>> driver to the C driver (in terms of IOPS) is between 6.8 and -11.8 percent with
>> an average of 0.2 percent better for reads. For writes the span is 16.8 to -4.5
>> percent with an average of 0.9 percent better.
>> 
>> For each measurement the drivers are loaded, a drive is configured with memory
>> backing and a size of 4 GiB. C null_blk is configured to match the implemented
>> modes of the Rust driver: `blocksize` is set to 4 KiB, `completion_nsec` to 0,
>> `irqmode` to 0 (IRQ_NONE), `queue_mode` to 2 (MQ), `hw_queue_depth` to 256 and
>> `memory_backed` to 1. For both the drivers, the queue scheduler is set to
>> `none`. These measurements are made using 30 second runs of `fio` with the
>> `PSYNC` IO engine with workers pinned to separate CPU cores. The measurements
>> are done inside a virtual machine (qemu/kvm) on an Intel Alder Lake workstation
>> (i5-12600).
>
> Hi All!
> I have some problems about your benchmark test.
> In Ubuntu 22.02, I compiled an RFL kernel with both C null_blk driver and Rust
> null_blk_driver as modules. For the C null_blk driver, I used the `modprobe`
> command to set relevant parameters, while for the Rust null_blk_driver, I simply
> started it. I used the following two commands to start the drivers:
>
> ```bash
> sudo modprobe null_blk \
>     queue_mode=2 irqmode=0 hw_queue_depth=256 \
>     memory_backed=1 bs=4096 completion_nsec=0 \
>     no_sched=1 gb=4;
> sudo modprobe rnull_mod
> ```
>
> After that, I tested their performance in `randread` with the fio command, specifying the first parameter as 4 and the second parameter as 1:
>
> ```bash
> fio --filename=/dev/nullb0 --iodepth=64 --ioengine=psync --direct=1 --rw=randread --bs=$1k --numjobs=$2 --runtime=30 --group_reporting --name=test-rand-read --output=test_c_randread.log
> fio --filename=/dev/rnullb0 --iodepth=64 --ioengine=psync --direct=1 --rw=randread --bs=$1k --numjobs=$2 --runtime=30 --group_reporting --name=test-rand-read --output=test_rust_randread.log
> ```
>
> The test results showed a significant performance difference between the two
> drivers, which was drastically different from the data you tested in the
> community. Specifically, for `randread`, the C driver had a bandwidth of
> 487MiB/s and IOPS of 124.7k, while the Rust driver had a bandwidth of 264MiB/s
> and IOPS of 67.7k. However, for other I/O types, the performance of the C and
> Rust drivers was more similar. Could you please provide more information about
> the actual bandwidth and IOPS data from your tests, rather than just the
> performance difference between the C and Rust drivers? Additionally, if you
> could offer possible reasons for this abnormality, I would greatly appreciate
> it!

Thanks for trying out the code! I am not sure why you get these numbers.
I am currently out of office, but I will rerun the benchmarks next week
when I get back in. Maybe I can provide you with some scripts and my
kernel configuration. Hopefully we can figure out the difference in our
setups.

Best regards,
Andreas