On Sat, Sep 26, 2020 at 01:11:50PM -0500, YiFei Zhu wrote: > On Fri, Sep 25, 2020 at 2:07 AM YiFei Zhu <zhuyifei1999@xxxxxxxxx> wrote: > > I'll try to profile the latter later on my qemu-kvm, with a recent > > libsecomp with binary tree and docker's profile, probably both direct > > filter attaches and filter attaches with fork(). I'm guessing if I > > have fork() the cost of fork() will overshadow seccomp() though. > > I'm surprised. That is not the case as far as I can tell. > > I wrote a benchmark [1] that would fork() and in the child attach a > seccomp filter, look at the CLOCK_MONOTONIC difference, then add it to > a struct timespec shared with the parent. It checks the difference > with the timespec before prctl and before fork. CLOCK_MONOTONIC > instead of CLOCK_PROCESS_CPUTIME_ID because of fork. > > I ran `./seccomp_emu_bench 100000` in my qemu-kvm and here are the results: > without emulator: > Benchmarking 100000 syscalls... > 19799663603 (19.8s) > seecomp attach without fork: 197996 ns > 33911173847 (33.9s) > seecomp attach with fork: 339111 ns > > with emulator: > Benchmarking 100000 syscalls... > 54428289147 (54.4s) > seecomp attach without fork: 544282 ns > 69494235408 (69.5s) > seecomp attach with fork: 694942 ns > > fork seems to take around 150us, seccomp attach takes around 200us, > and the filter emulation overhead is around 350us. I had no idea that > fork was this fast. If I wrote my benchmark badly please criticise. You're calling clock_gettime() inside your loop. That might change the numbers. Why not just measure outside the loop, or better yet, use "perf" to measure the time in prctl(). > Given that we are doubling the time to fork() + seccomp attach filter, > I think yeah running the emulator on the first instance of a syscall, > holding a lock, is a much better idea. If I naively divide 350us by > the number of syscall + arch pairs emulated the overhead is less than > 1 us and that should be okay since it only happens for the first > invocation of the particular syscall. > > [1] https://gist.github.com/zhuyifei1999/d7bee62bea14187e150fef59db8e30b1 Regardless, let's take things one step at a time. First, let's do the simplest version of the feature, and then let's look at further optimizations. Can you send a v3 and we can continue from there? -- Kees Cook
