On Thu, Oct 3, 2019 at 8:09 PM Roman Gushchin <g...@fb.com> wrote: > > On Wed, Oct 02, 2019 at 05:59:36PM -0400, Bruce Ashfield wrote: > > On Wed, Oct 2, 2019 at 2:19 PM Roman Gushchin <g...@fb.com> wrote: > > > > > > On Wed, Oct 02, 2019 at 12:18:54AM -0400, Bruce Ashfield wrote: > > > > On Tue, Oct 1, 2019 at 10:01 PM Roman Gushchin <g...@fb.com> wrote: > > > > > > > > > > On Tue, Oct 01, 2019 at 12:14:18PM -0400, Bruce Ashfield wrote: > > > > > > Hi all, > > > > > > > > > > > > > > > > Hi Bruce! > > > > > > > > > > > The Yocto project has an upcoming release this fall, and I've been > > > > > > trying to > > > > > > sort through some issues that are happening with kernel 5.2+ .. > > > > > > although > > > > > > there is a specific yocto kernel, I'm testing and seeing this with > > > > > > normal / vanilla > > > > > > mainline kernels as well. > > > > > > > > > > > > I'm running into an issue that is *very* similar to the one > > > > > > discussed in the > > > > > > [REGRESSION] ptrace broken from "cgroup: cgroup v2 freezer" > > > > > > (76f969e) > > > > > > thread from this past may: https://lkml.org/lkml/2019/5/12/272 > > > > > > > > > > > > I can confirm that I have the proposed fix for the initial > > > > > > regression report in > > > > > > my build (05b2892637 [signal: unconditionally leave the frozen state > > > > > > in ptrace_stop()]), > > > > > > but yet I'm still seeing 3 or 4 minute runtimes on a test that used > > > > > > to take 3 or > > > > > > 4 seconds. > > > > > > > > > > So, the problem is that you're experiencing a severe performance > > > > > regression > > > > > in some test, right? > > > > > > > > Hi Roman, > > > > > > > > Correct. In particular, running some of the tests that ship with strace > > > > itself. > > > > The performance change is so drastic, that it definitely makes you > > > > wonder > > > > "What have I done wrong? Since everyone must be seeing this" .. and I > > > > always blame myself first. > > > > > > > > > > > > > > > > > > > > > This isn't my normal area of kernel hacking, so I've so far come up > > > > > > empty > > > > > > at either fixing it myself, or figuring out a viable workaround. > > > > > > (well, I can > > > > > > "fix" it by remove the cgroup_enter_frozen() call in ptrace_stop ... > > > > > > but obviously, > > > > > > that is just me trying to figure out what could be causing the > > > > > > issue). > > > > > > > > > > > > As part of the release, we run tests that come with various > > > > > > applications. The > > > > > > ptrace test that is causing us issues can be boiled down to this: > > > > > > > > > > > > $ cd /usr/lib/strace/ptest/tests > > > > > > $ time ../strace -o log -qq -esignal=none -e/clock > > > > > > ./printpath-umovestr>ttt > > > > > > > > > > > > (I can provide as many details as needed, but I wanted to keep this > > > > > > initial > > > > > > email relatively short). > > > > > > > > > > > > I'll continue to debug and attempt to fix this myself, but I > > > > > > grabbed the > > > > > > email list from the regression report in May to see if anyone has > > > > > > any ideas > > > > > > or angles that I haven't covered in my search for a fix. > > > > > > > > > > I'm definitely happy to help, but it's a bit hard to say anything > > > > > from what > > > > > you've provided. I'm not aware of any open issues with the freezer > > > > > except > > > > > some spurious cgroup frozen<->not frozen transitions which can happen > > > > > in some > > > > > cases. If you'll describe how can I reproduce the issue, and I'll try > > > > > to take > > > > > a look asap. > > > > > > > > That would be great. > > > > > > > > I'll attempt to remove all of the build system specifics out of this > > > > (and Richard Purdie > > > > on the cc' of this can probably help provide more details / setup info > > > > as well). > > > > > > > > We are running the built-in tests of strace. So here's a cut and paste > > > > of what I > > > > did to get the tests available (ignore/skip what is common sense or > > > > isn't needed > > > > in your test rig). > > > > > > > > % git clone https://github.com/strace/strace.git > > > > % cd strace > > > > % ./bootstrap > > > > # the --enable flag isn't strictly required, but may break on some > > > > build machines > > > > % ./configure --enable-mpers=no > > > > % make > > > > % make check-TESTS > > > > > > > > That last step will not only build the tests, but run them all .. so > > > > ^c the run once > > > > it starts, since it is a lot of noise (we carry a patch to strace that > > > > allows us to build > > > > the tests without running them). > > > > > > > > % cd tests > > > > % time strace -o log -qq -esignal=none -e/clock ./printpath-umovestr > > > > > fff > > > > real 0m2.566s > > > > user 0m0.284s > > > > sys 0m2.519 > > > > > > > > On pre-cgroup2 freezer kernels, you see a run time similar to what I > > > > have above. > > > > On the newer kernels we are testing, it is taking 3 or 4 minutes to > > > > run the test. > > > > > > > > I hope that is simple enough to setup and try. Since I've been seeing > > > > this on both > > > > mainline kernels and the yocto reference kernels, I don't think it is > > > > something that > > > > I'm carrying in the distro/reference kernel that is causing this (but > > > > again, I always > > > > blame myself first). If you don't see that same run time, then that > > > > does point the finger > > > > back at what we are doing and I'll have to apologize for chewing up > > > > some of your > > > > time. > > > > > > Thank you for the detailed description! > > > I'll try to reproduce the issue and will be back > > > by the end of the week. > > > > Thanks again! > > > > While discussing the issue with a few yocto folks today, it came up that > > someone wasn't seeing the same behaviour on the opensuse v5.2 kernel > > (but I've yet to figure out exactly where to find that tree) .. but when I > > do, > > I'll try and confirm that and will look for patches or config differences > > that > > could explain the results. > > > > I did confirm that 5.3 shows the same thing today, and I'll do a 5.4-rc1 > > test > > tomorrow. > > > > We are also primarily reproducing the issue on qemux86-64, so I'm also > > going to try and rule out qemu (but the same version of qemu with just > > the kernel changing shows the issue). > > Hi Bruce! > > I've tried to follow your steps, but unfortunately failed to reproduce the > issue. > I've executed the test on my desktop running 5.2 and cgroup v1 (Fedora 30), > and also a qemu vm with vanilla 5.1 and 5.3 and cgroup v2 mounted by default. > In all cases the test execution time was about 4.5 seconds.
Hi Roman, Thanks for the time you spent on this. I had *thought* that I ruled out my config before posting .. but clearly, it is either not my config or something else in the environment. > > Looks like something makes your setup special. If you'll provide your > build config, qemu arguments or any other configuration files, I can try > to reproduce it on my side. Indeed. I'm going to dive back in and see what I can find. If I can find something that is reproducible in a completely different environment and easy to configure components, I'll follow up with details. When I figure out what is going on with the config here, I'll follow up as well, so the solution can be captured in any archives. Thanks again, Bruce > > Thanks! > > Roman -- - Thou shalt not follow the NULL pointer, for chaos and madness await thee at its end - "Use the force Harry" - Gandalf, Star Trek II
