https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240121
Bug ID: 240121
Summary: Serial console can eat a lot of cpu with law baudrate
Product: Base System
Version: 11.2-RELEASE
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: [email protected]
Reporter: [email protected]
Since https://svnweb.freebsd.org/base?view=revision&revision=317659, devices
connected through a serial device and using a low baudrate seems to eat a lot
more cpu than before.
This has been constated using a lcd screen with a baudrate of 2400.
Using pmc, I got this:
PMC: [CPU_CLK_UNHALTED.THREAD_P] Samples: 14 (100.0%) , 0 unresolved
%SAMP CALLTREE
85.7 amd64_syscall@kernel sys_write kern_writev dofilewrite devfs_write_f
ttydev_write ttydisc_write tty_wait _cv_wait_sig __mtx_lock_sleep
lock_delay(85.7%)
7.1 _start@xxx <no relevent information here>(7.1%)
7.1 _start@xxx <no relevent information here>(7.1%)
Reverting this commit made the call to lock_delay disappear and the
performances of my test system back to normal.
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