On 4/28/21 2:32 PM, Hao Xu wrote:
> currently unit of io_sq_thread_idle is millisecond, the smallest value
> is 1ms, which means for IOPS > 1000, sqthread will very likely take
> 100% cpu usage. This is not necessary in some cases, like users may
> don't care about latency much in low IO pressure
> (like 1000 < IOPS < 20000), but cpu resource does matter. So we offer
> an option of nanosecond granularity of io_sq_thread_idle. Some test
> results by fio below:
If numbers justify it, I don't see why not do it in ns, but I'd suggest
to get rid of all the mess and simply convert to jiffies during ring
creation (i.e. nsecs_to_jiffies64()), and leave io_sq_thread() unchanged.
Or is there a reason for having it high precision, i.e. ktime()?
> uring average latency:(us)
> iops\idle 10us 60us 110us 160us 210us 260us 310us 360us 410us 460us 510us
> 2k 10.93 10.68 10.72 10.7 10.79 10.52 10.59 10.54 10.47 10.39 8.4
> 4k 10.55 10.48 10.51 10.42 10.35 8.34
> 6k 10.82 10.5 10.39 8.4
> 8k 10.44 10.45 10.34 8.39
> 10k 10.45 10.39 8.33
>
> uring cpu usage of sqthread:
> iops\idle 10us 60us 110us 160us 210us 260us 310us 360us 410us 460us 510us
> 2k 4% 14% 24% 34.70% 44.70% 55% 65.10% 75.40% 85.40% 95.70% 100%
> 4k 7.70% 28.20% 48.50% 69% 90% 100%
> 6k 11.30% 42% 73% 100%
> 8k 15.30% 56.30% 97% 100%
> 10k 19% 70% 100%
>
> aio average latency:(us)
> iops latency 99th lat cpu
> 2k 13.34 14.272 3%
> 4k 13.195 14.016 7%
> 6k 13.29 14.656 9.70%
> 8k 13.2 14.656 12.70%
> 10k 13.2 15 17%
>
> fio config is:
> ./run_fio.sh
> fio \
> --ioengine=io_uring --sqthread_poll=1 --hipri=1 --thread=1 --bs=4k \
> --direct=1 --rw=randread --time_based=1 --runtime=300 \
> --group_reporting=1 --filename=/dev/nvme1n1 --sqthread_poll_cpu=30 \
> --randrepeat=0 --cpus_allowed=35 --iodepth=128 --rate_iops=${1} \
> --io_sq_thread_idle=${2}
>
> in 2k IOPS, if latency of 10.93us is acceptable for an application,
> then they get 100% - 4% = 96% reduction of cpu usage, while the latency
> is smaller than aio(10.93us vs 13.34us).
>
> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
> ---
[snip]
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index e1ae46683301..311532ff6ce3 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -98,6 +98,7 @@ enum {
> #define IORING_SETUP_CLAMP (1U << 4) /* clamp SQ/CQ ring sizes */
> #define IORING_SETUP_ATTACH_WQ (1U << 5) /* attach to existing wq */
> #define IORING_SETUP_R_DISABLED (1U << 6) /* start with ring disabled */
> +#define IORING_SETUP_IDLE_NS (1U << 7) /* unit of thread_idle is nano second */
>
> enum {
> IORING_OP_NOP,
> @@ -259,7 +260,7 @@ struct io_uring_params {
> __u32 cq_entries;
> __u32 flags;
> __u32 sq_thread_cpu;
> - __u32 sq_thread_idle;
> + __u64 sq_thread_idle;
breaks userspace API
> __u32 features;
> __u32 wq_fd;
> __u32 resv[3];
>
--
Pavel Begunkov
