How can I get 99.99th latency? about femu HOT 2 CLOSED

Can you let me know how to measure 99.99th long tail latency?
Is it possible to measure latency of each I/O?

In your guest OS, you can run IO benchmark tools (e.g. FIO) to measure per-IO latencies (by enabling the per-IO latency log option "write_lat_log"), then you can calculate the CDF by yourself (e.g. I have a small tool here for that purpose: https://github.com/huaicheng/rtk). FIO output also contains some predefined percentiles.

Is it right that latency measurements in femu are made by recording in specific memory rather than delaying through 'sleep' command? I want to know exactly how measurements are made in femu.

In general, FEMU emulates IO delay transparent to the applications running in the guest OS. FEMU delay each IO for a certain amount of time before it returns the IO back to guest OS. The time to delay is decided by the FTL logic based on NAND latencies and queueing delays.

from femu.

thank you for your reply!

from femu.