On Thu, Jun 23, 2022 at 9:42 AM Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote: > > On 6/22/22 09:24, Song Liu wrote: > > This is interesting work! > > > > I applied the series on top of commit 78ca55889a549a9a194c6ec666836329b774ab6d > > in upstream. Then, I got some compile/link error for CONFIG_RV_MON_WIP and > > CONFIG_RV_MON_SAFE_WTD. I was able to compile the kernel with these two > > configs disabled. > > I rebased the code and... it compiled. Maybe it was missing some > config options that I forgot to set as "depends on" in the Kconfig. > > Can you check if it was the same problem automatically reported? > > Any further information here would help. I will revisit this. Here are the error messages I got: https://pastebin.com/zJxMA6RK , and attached is the config file I used. > > However, I hit the some issue with monitors/wwnr/enabled : > > > > [root@eth50-1 ~]# cd /sys/kernel/debug/tracing/rv/ > > [root@eth50-1 rv]# cat available_monitors > > wwnr > > [root@eth50-1 rv]# echo wwnr > enabled_monitors > > [root@eth50-1 rv]# cd monitors/ > > [root@eth50-1 monitors]# cd wwnr/ > > [root@eth50-1 wwnr]# ls > > desc enable reactors > > [root@eth50-1 wwnr]# cat enable > > 1 > > [root@eth50-1 wwnr]# echo 0 > enable <<< hangs > > > > The last echo command hangs forever on a qemu vm. I haven't figured out why > > this happens though. > > I could reproduce it. It is an error in the return code of monitor_enable_write_data(), > I fixed it locally (return retval ? retval : count; // needs more test), and > will add it to the next version. Thanks! > > > I also have a more general question: can we do RV with BPF and simplify the > > work? AFAICT, the idea of RV is to maintain a state machine based on events. > > If something unexpected happens, call the reactor. > > > > IIUC, BPF has most of these building blocks ready for use. With BPF, we > > can ship many RV monitors without much kernel changes. > > I am aware of bpftrace and bpf + libbpf, and I have a PoC tool doing most of the > work I do in C/kernel in C/bpf. > > From the cover letter: > > "Things kept for a second moment (after this patchset): > [...] > - dot2bpf" > > The point is that there are use-cases in which the users need the code in > C. One of those is the work being done in the Linux Foundation Elisa group. > There will be more formalism, like timed automata... which will require > infra-structure that is easily accessible in C... including synchronization, > and reactors that are available only in C on "per use-cases" basis - for > example on embedded devices. Where can I find more information about the constraints of these use cases? I am asking because there are multiple ways to load a BPF program to the system. If the constraint is that we cannot have bpftrace or bcc in the system, maybe it is ok to run a standalone binary (written in C, compiled on a different system). Or maybe we can load BPF programs in a kernel module, or compile the BPF programs into the kernel? (Yes, we can do it now, check kernel/bpf/preload). If any of these works, we can benefit from the good properties of BPF. For example, we can update the RV models without rebooting the system; and we can reuse various BPF maps, so we don't need to add union rv_task_monitor to task_struct. Of course, we are out of luck if these systems cannot enable CONFIG_BPF at all. But I guess this is not common for modern embedded systems? Thanks, Song
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