On Wed, Oct 19, 2022 at 10:11:58PM +0800, Leizhen (ThunderTown) wrote: > > > 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. This answers how we don't use a hash table, the question was *should* we use one? Luis
