Hello,
I have done some measurments using oprofile while running
loopback test for my comm driver.
Result 1.
<cnt> < % >
0001cc60 12931 3.95405 .text.lock.KBUILD_BASENAME
00014d24 16618 5.08146 lis_atomic_read
0001c6f8 35473 10.847 lis_spin_lock_irqsave_fcn
0001c750 36925 11.2909 lis_spin_unlock_irqrestore_fcn
00014d4c 38526 11.7805% lis_atomic_dec
00014d44 104768 32.036% lis_atomic_inc
I.e. lis_atomic_(inc/dec) chewed 44% of CPU while in streams module!!!
In order to see where those lis_atomic dudes are called from
I redifined them from functions to text definitions.
(Actually that is a beneficial thing on its own,
lis_atomic_xxx() function calling just atomic_xxx() is a bit
of an overkill)
Result 2.
001c038 17193 3.00437 lis_rw_read_lock_irqsave_fcn
0018388 19254 3.36451 LisUpCounter
001bd2c 22249 3.88787 lis_spin_lock_fcn
001be7c 133388 23.3087 lis_spin_unlock_irqrestore_fcn
001be34 206767 36.1312 lis_spin_lock_irqsave_fcn
Now it spreaded to the lock functions.
So, I have commented out lis_atomic_inc(&lis_spin_lock_count) and
if (spin_is_locked(l))
lis_atomic_inc(&lis_spin_lock_contention_count) ;
from lis_spin_lock_irqsave_fcn() and couple of other functions.
I have also commented out statistic gathering from LisUpCounter()
that uses a bunch of atomic_xxx() calls.
Result 3.
<cnt> < % >
0001bcdc 20331 3.25159 lis_spin_lock_fcn
0001bfb0 20438 3.2687 lis_rw_read_lock_irqsave_fcn
0001bdf4 162768 26.0319 lis_spin_unlock_irqrestore_fcn
0001bdc8 168222 26.9042 lis_spin_lock_irqsave_fcn
As it can be seen, that resulted in 10% saving for
the lis_spin_lock_irqsave_fcn() execution.
Overall, I have added 7% to the idle time doing the same test.
Shouldn't it be beneficial to add #ifdef CONFIG_DEV
around statistic gathering in the aforementioned code places?
Replacing lis_atomic_xx() functions with text defs?
--
Eugene
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