在 2023/6/23 18:03, Paul Menzel 写道:
Dear Li,
Thank you for your patch.
Am 23.06.23 um 19:32 schrieb linan666@xxxxxxxxxxxxxxx:
From: Li Nan <linan122@xxxxxxxxxx>
We dereference r10_bio->read_slot too many times in fix_read_error().
Optimize it by using a variable to store read_slot.
I am always cautious reading about optimizations without any benchmarks
or object code analysis. Although your explanation makes sense, did you
check, that performance didn’t decrease in some way? (Maybe the compiler
even generates the same code.)
Kind regards,
Paul
Compared assembly code before and after optimization:
- With gcc 8.3.0, both are consistent.
- With gcc 12.2.1, 'r10_bio->read_slot' mostly uses r10bio dirctly:
2853 while (sl != r10_bio->read_slot) {
0xffffffff8213f2a0 <+1328>: cmp %r14d,0x38(%rbp)
'slot' is mostly saved to a register individually:
2819 while (sl != slot) {
0xffffffff8213f08a <+794>: cmp %r14d,%ebx
I have not tested the performance, and it won't bring significant
performance optimization, which can also be seen from the analysis of
the assembly code. In fact, I just want to make code more readable.
--
Thanks,
Nan
