Hi,
on a ARMv7 Freescale i.MX6 based system we are looking at optimizing the
kernel boot time. Booting a 3.5.7 kernel with SMP=y and the kernel
option 'nosmp' (the i.MX6 has single, dual and quad CPU versions) we get
[ 0.255927] hw perfevents: enabled with ARMv7 Cortex-A9 PMU driver, 7
counters available
[ 0.256033] Setting up static identity map for 0x10426a28 - 0x10426a80
[ 0.260204] initcall spawn_ksoftirqd+0x0/0x58 returned 0 after 9765 usecs
[ 0.270363] initcall init_workqueues+0x0/0x39c returned 0 after 9765
usecs
[ 0.290265] initcall cpu_stop_init+0x0/0xd0 returned 0 after 19531 usecs
[ 0.310449] initcall rcu_spawn_kthreads+0x0/0xc0 returned 0 after
19531 usecs
[ 0.310699] Brought up 1 CPUs
[ 0.310712] SMP: Total of 1 processors activated (1581.05 BogoMIPS).
I.e. ~55ms just for bringing up the 1 CPU.
Looking into some details, e.g. cpu_stop_init(), the ~19531 usecs are
there because the system 'hangs' 2 jiffies (CONFIG_HZ=100) in
cpu_v7_do_idle().
For testing purposes switching to CONFIG_HZ=1000 reduces above 54ms to
just ~4ms. But we are unsure to switch the whole system to
CONFIG_HZ=1000 just to optimize this part of the boot process.
Does anybody know why all the above parts are idling for some jiffies?
Is there any other optimization than CONFIG_HZ=1000 possible?
In case there are any patches floating around or this was already
discussed, any link would be nice.
Many thanks and best regards
Dirk
--
To unsubscribe from this list: send the line "unsubscribe linux-embedded" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
