rngd consumes CPU for a few minutes after BMC boot

Question

rngd consumes CPU for a few minutes after BMC boot

Closed this issue 4 years ago · 9 comments

Note on Bugs
After BMC is booted (or rebooted), rngd consumes a lot of CPU for a few minutes.

Unexpected behavior you saw

# top
  318     1 root     RN   12244   2%  70% /usr/sbin/rngd -f -r /dev/hwrng

Expected behavior
rngd shall not consume so much CPU

To Reproduce
Steps to reproduce the behavior:

Build intel-bmc/openbmc (either intel or update branch), flash to CRB.
Boot CRB's BMC, or reboot the BMC
Login to BMC's debug console, use top to check the CPU usage
During a few minutes, we could see /usr/sbin/rngd process consumes a lot of CPU

Additional context
Be noted that there is a related issue in upstream: openbmc/openbmc#3574, but with the issue fixed, the rngd process still consumes CPU at start until the entropy poll is filled.

Answer 1 · 2020-05-19T02:13:32.000Z

Can not reproduce it. How long could it last from your observation?

Answer 2 · 2020-05-19T02:29:24.000Z

It usually takes 2~3 minutes after BMC boot/reboot.

Answer 3 · 2020-05-19T02:31:05.000Z

Then it does not match what I observe. I see 70% once but it lasts only for around 1 second.

Answer 4 · 2020-05-19T02:35:56.000Z

intel-BMC already contains the fix for openbmc/openbmc#3574

Answer 5 · 2020-05-19T02:42:26.000Z

Then it does not match what I observe. I see 70% once but it lasts only for around 1 second.

Do you mean the CRB image or the open-sourced build?

intel-BMC already contains the fix for openbmc/openbmc#3574

Yup, this issue is a separated one. The issue in the above link is for the rngd consumes CPU forever.
This issue is for the rngd consumes CPU for a few minutes after BMC boots/reboots.

Answer 6 · 2020-05-19T02:46:11.000Z

This build. intel-BMC. I built the open source image and test it on CRB.

Answer 7 · 2020-05-19T05:11:57.000Z

Verified that on ca9404e the issue still occurs.
Updated a log captured from top -d1.
top.log

Be noted that after BMC reboot/boot, there are other processes consuming CPU at first, e.g. entity-manager, bmcweb, etc, and after a while (about 20~30 seconds), the services are done, and we could see rngd consuming the CPU.

Answer 8 · 2020-05-20T04:44:13.000Z

Isn't it as expected that rngd is consuming CPU? Basically, it needs CPU resource to finish initialiation.
We checked that rngd service has lower priority than entity-manager, bmcweb. It matches what you observed. rngd will start to eat more resource right after these processes are ready (finishing initialization).

Answer 9 · 2020-05-20T05:18:40.000Z

Right, I realize that the upstream OpenBMC has the same behavior.
Close this.