On 2022/10/19 20:01, Luis Chamberlain wrote: > On Mon, Oct 17, 2022 at 02:49:39PM +0800, Zhen Lei wrote: >> Currently, to search for a symbol, we need to expand the symbols in >> 'kallsyms_names' one by one, and then use the expanded string for >> comparison. This is very slow. >> >> In fact, we can first compress the name being looked up and then use >> it for comparison when traversing 'kallsyms_names'. >> >> This patch series optimizes the performance of function kallsyms_lookup_name(), >> and function klp_find_object_symbol() in the livepatch module. Based on the >> test results, the performance overhead is reduced to 5%. That is, the >> performance of these functions is improved by 20 times. > > Stupid question, is a hash table in order? No hash table. All symbols are arranged in ascending order of address. For example: cat /proc/kallsyms The addresses of all symbols are stored in kallsyms_addresses[], and names of all symbols are stored in kallsyms_names[]. The elements in these two arrays are in a one-to-one relationship. For any symbol, it has the same index in both arrays. Therefore, when we look up a symbolic name based on an address, we use a binary lookup. However, when we look up an address based on a symbol name, we can only traverse array kallsyms_names[] in sequence. I think the reason why hash is not used is to save memory. > > Luis > . > -- Regards, Zhen Lei
