[Letux-kernel] jz4730-i2c - clocksource

[H. Nikolaus Schaller]

Hi Paul,
seems as if I can now also boot with clocksource=ingenic-timer without problems.

So avoiding regmap and using at least 26 bits (I also want to check 32 bit again)
makes it work.

BTW: there is one more fix: I am resetting the Underrun flag in the interrupt
handler. Maybe this prevents that the IRQ stays activated or is still active
immediately if a new timer request is written. But I have not checked if this is
really needed.

> Am 06.03.2021 um 12:03 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> 	sysbench --num-threads=1 --test=cpu --cpu-max-prime=1 run

I just had the idea to run this through strace :)

futex(0x777954f8, FUTEX_WAIT, 3116, NULL) = 0

can be seen on i.MX6 and on jz4730. But on jz4730 it takes ca. 15 seconds to succeed while i.MX6 it is not noticeable.

A little more specific:

i.MX6:

clock_gettime(CLOCK_REALTIME, {1615034730, 819353480}) = 0
mmap2(NULL, 32768, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0xb6f81000
mprotect(0xb6f81000, 4096, PROT_NONE)   = 0
clone(child_stack=0xb6f87f88, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0xb6f884b8, tls=0xb6f88910, child_tidptr=0xb6f884b8) = 24026
write(1, "Threads started!\n", 17Threads started!
)      = 17
futex(0xb6f884b8, FUTEX_WAIT, 24026, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 0}}, {it_interval={0, 0}, it_value={0, 0}}) = 0
write(1, "Done.\n\n", 7Done.

)                = 7
clock_gettime(CLOCK_REALTIME, {1615034730, 883641481}) = 0

jz4730:

clock_gettime(CLOCK_REALTIME, {1615035340, 801868585}) = 0
mmap(NULL, 8388608, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x76f96000
mprotect(0x76f96000, 4096, PROT_NONE)   = 0
clone(child_stack=0x77794ff0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x777954f8, tls=0x7779c920, child_tidptr=0x777954f8) = 3116
write(1, "Threads started!\n", 17Threads started!
)      = 17
futex(0x777954f8, FUTEX_WAIT, 3116, NULL) = 0
alarm(0)                                = 0
write(1, "Done.\n\n", 7Done.

)                = 7
clock_gettime(CLOCK_REALTIME, {1615035356, 871232080}) = 0


What we can see is that ARM uses mmap2() and setitimer() while MIPS uses mmap() and alarm().
Otherwise there is no visible difference - besides the 15 seconds delay of the futex.

This seems to be a new research project:
a) what is the futex doing in sysbench (where is it hidden)?
b) how is futex implemented on jz4730?
c) why does it block that long?

Maybe this is also the reason why X11 is that slow.

BR,
Nikolaus