On Thu, 16 Jan 2025 13:04:18 +0100 Daniel Wagner <dwag...@suse.de> wrote:
> On Thu, Jan 16, 2025 at 08:48:18AM +0900, Masami Hiramatsu wrote: > > Have you tried to use `perf probe`? Even if it is inlined, you can find them > > by > > > > perf probe -a nvme_change_ctrl_state new_state > > I had to build my own perf, as the version from the distro didn't like > my kernel and just crashed. Thus I added a bunch libraries to my build > system. The resulting perf installed the probe and the missing events > show up: > > <idle>-0 [000] ..s1. 245.406139: nvme_complete_rq: nvme1: > qid=0, cmdid=36865, res=0x0, retries=0, flags=0x0, status=0x371 > <idle>-0 [000] .Ns1. 245.407192: nvme_change_ctrl_state: > (nvme_change_ctrl_state+0x0/0x180 [nvme_core]) new_state=0x2 > kworker/u33:0-65 [000] .N... 245.407258: nvme_change_ctrl_state: > (nvme_change_ctrl_state+0x0/0x180 [nvme_core]) new_state=0x2 > kworker/u33:1-78 [000] ..... 245.421290: nvme_change_ctrl_state: > (nvme_change_ctrl_state+0x0/0x180 [nvme_core]) new_state=0x3 > Nice. > I double checked my previous setup with kprobes and now the missing > events show up as well. It looks like my setup changes makes clang to > not inline this function anymore, or there is no additional debug info > available? Hmm, I don't think (don't hope) the clang change the optimization silently if debuginfo is enabled. This is a kind of heisenbug :( > > > But perhaps, some of them are inlined with constant numbers (maybe you can > > find them as nvme_change_ctrl_state.constprop.XXX in kallsyms) > > # cat /proc/kallsyms | grep nvme_change_ctrl_state > ffffffffc03dc04d r __kstrtab_nvme_change_ctrl_state [nvme_core] > ffffffffc03dc064 r __kstrtabns_nvme_change_ctrl_state [nvme_core] > ffffffffc03ca130 r __ksymtab_nvme_change_ctrl_state [nvme_core] > ffffffffc0405de0 t __pfx_nvme_change_ctrl_state [nvme_core] > ffffffffc0405df0 t nvme_change_ctrl_state [nvme_core] > > This is with the new kernel, so after installing the libraries for the > perf build. IIRC, constprop.XXX is gcc's suffix, clang has different one. > > > If my guess is correct, it is not inlined but the constant propagation > > optimization[1] has been done by the compiler. > > > > [1] https://en.wikipedia.org/wiki/Constant_folding#Constant_propagation > > > > IIRC, commit 66f69b219716 ("perf probe: Support DW_AT_const_value constant > > value") > > should support this case. > > Okay, this commit is already in (v5.4), so it was always in. > > Anyway, I can't reproduce anymore. Feel free to notice if you see similar issue. Thank you, > > Daniel -- Masami Hiramatsu (Google) <mhira...@kernel.org>
