On 5/9/2017 8:39 PM, Jiri Olsa wrote:
On Tue, May 09, 2017 at 07:57:11PM +0800, Jin, Yao wrote:
SNIP
+
+ type >>= 2; /* skip X86_BR_USER and X86_BR_KERNEL */
+ mask = ~(~0 << 1);
is that a fancy way to get 1 into the mask? what do I miss?
you did not comment on this one
Sorry, I misunderstood that this comment and the next comment had the same
meaning.
In the previous version, I used the switch/case to convert from X86_BR to
PERF_BR. I got a comment from community that it'd better use a lookup table
for conversion.
Since each bit in type represents a X86_BR type so I use a mask (0x1) to
filter the bit. Yes, it looks I can also directly set 0x1 to mask.
I write the code "mask = ~(~0 << 1)" according to my coding habits. If you
think I should change the code to "mask = 0x1", that's OK :)
im ok with that.. was just wondering for the reason
I guess compiler will make it single constant assignment anyway
I think so. The compiler should be clever enough for this optimization.
+
+ for (i = 0; i < X86_BR_TYPE_MAP_MAX; i++) {
+ if (type & mask)
+ return branch_map[i];
I wonder some bit search would be faster in here, but maybe not big deal
jirka
I just think the branch_map[] doesn't contain many entries (16 entries
here), so maybe checking 1 bit one time should be acceptable. I just want to
keep the code simple.
But if the number of entries is more (e.g. 64), maybe it'd better check 2 or
4 bits one time.
ook
jirka
Sorry, what's the meaning of ook? Does it mean "OK"?
just means ok ;-)
thanks,
jirka
Thanks so much!
Jin Yao
