Re: [RESEND PATCH 0/5] perf core: Support overwrite ring buffer

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Mar 08, 2016 at 02:49:01PM +0100, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Mon, Mar 07, 2016 at 03:50:14AM +0000, Wang Nan wrote:
> > > This patch set has been posted multiple times (with and without
> > > corresponding 'perf tool' patches), and doesn't receive further
> > > comment. I think it should be okay to merge them into mainline.
> > > There are many perf's improvement depend on it. However, Peter
> > > is not responsive after I fixed some problems he pointed out.
> > > 
> > > Introduces 'write_backward' into perf_event_attr, allows kernel
> > > writing the ring buffer from the end of it. This feature allows
> > > extracting data from overwritable ring buffer.
> > > 
> > > Wang Nan (5):
> > >   perf core: Introduce new ioctl options to pause and resume ring buffer
> > >   perf core: Set event's default overflow_handler
> > >   perf core: Prepare writing into ring buffer from end
> > >   perf core: Add backward attribute to perf event
> > >   perf core: Reduce perf event output overhead by new overflow handler
> > 
> > perf kernel features are currently on hold until I can manage to run a
> > fuzzer for more than a few minutes without my machine having a seizure.
> 
> Btw., could you describe exactly what commands you are running, with what 
> configuration options (if that matters), so that people who'd like our feature 
> freeze to be lifted can help out?

Mostly syz-kaller, but also Vince's perf-fuzzer and your perf-stress
script, which I'm not sure is publicly available.

perf_fuzzer lives at:

  https://github.com/deater/perf_event_tests.git

Here's a thread on syz-kaller:

  lkml.kernel.org/r/CACT4Y+Ym0TZLkmRrM0ZGgLpu8kqS-YjoWTMrvaLz=tx2tnyO3w@mail.gmail.com

If things have shifted again I'm sure Dmitry is willing to help.

I run the thing natively on actual real hardware, which ensure I get to
test the PMU drivers too.

# cat go-fuzz.sh
#!/bin/bash

echo 1 > /proc/sys/kernel/traceoff_on_warning
echo 1 > /debug/tracing/options/stacktrace
echo 1 > /debug/tracing/events/sched/enable
cd gopath/src/github.com/google/syzkaller/
./bin/syz-manager -config perf.cfg

# cat gopath/src/github.com/google/syzkaller/perf.cfg

{
        "http": "localhost:50000",
        "workdir": "/root/gopath/src/github.com/google/syzkaller/workdir",
        "syzkaller": "/root/gopath/src/github.com/google/syzkaller",
        "vmlinux": "-",
        "type": "local",
        "count": 1,
        "procs": 160,
        "cover": false,
        "dropprivs": false,
        "enable_syscalls": [
                "getpid",
                "gettid",
                "perf_event_open",
                "ioctl$PERF*",
                "prctl$void",
                "bpf$*",
                "sched_yield"
        ]
}