On Tue, Aug 9, 2016 at 9:59 AM, riya khanna <riyakhanna1...@gmail.com>
wrote:
> On Tue, Aug 9, 2016 at 12:24 PM, Brenden Blanco <bbla...@plumgrid.com>
> wrote:
> >
> >
> > On Tue, Aug 9, 2016 at 9:16 AM, riya khanna <riyakhanna1...@gmail.com>
> > wrote:
> >>
> >> On Tue, Aug 9, 2016 at 12:05 PM, Brenden Blanco <bbla...@plumgrid.com>
> >> wrote:
> >> > On Tue, Aug 9, 2016 at 8:54 AM, riya khanna <riyakhanna1...@gmail.com
> >
> >> > wrote:
> >> >>
> >> >> Hi Brenden,
> >> >>
> >> >> Saw test_perf_event.py in your branch. Its creates and enables per
> >> >> counters once during start. Is it also possible to
> >> >> enable/disable/reset counters on the fly? Perhaps we need a kernel
> >> >> patch for this?
> >> >
> >> > It doesn't "create" counters, it just attaches to the already
> available
> >> > counters provided by the hardware or OS.
> >>
> >> Yes, it enables monitoring when attached.
> >>
> >> > Any type of "reset" infrastructure
> >> > would adversely impact other users of those same counters (perf). I
> >> > consider
> >> > it the job of userspace or the program to compute deltas or other
> types
> >> > of
> >> > history.
> >>
> >> Well, there are limited counters. How to multiplex from userspace on
> >> the fly (e.g. monitoring a set of events first, followed by a
> >> different set)?
> >
> > I would just create a different BPF_PERF_ARRAY for each different one.
>
> Yes, but if you create more than available number of hardware counters
> (i.e. try to monitor more events concurrently than allowed by the
> hardware), counter value is reported as '0'. Verified with a test
> program (perf.c, attached) that uses perf_event_open() syscall.
> Depending upon the number of counters available on your platform,
> change NUM_REQ_HW_CNTRS to verify the behavior
>
> A way to enable/disable events at runtime will help userspace
> multiplex over available hardware counters and monitor more more
> events (similar to perf stat tool)
>
If you just call table.open_perf_event(NEW_TYPE) multiple times, it should
bind a new counter to the same table entry, allowing you to change the
monitored event over time. Have you tried that?
>
> >>
> >> Also, is it possible to handle counter overflow?
> >
> > What does it mean to "handle"? If computing deltas, for instance, the
> > subtraction will just underflow and wrap around to the correct value,
> > assuming the values are both unsigned.
> >>
> >>
> >> >>
> >> >>
> >> >> Thanks,
> >> >> Riya
> >> >>
> >> >> On Fri, Jul 29, 2016 at 1:57 PM, riya khanna <
> riyakhanna1...@gmail.com>
> >> >> wrote:
> >> >> > Thanks Brenden!
> >> >> >
> >> >> > I'm working with your branch for now. Additionally, I'm unable to
> >> >> > create software events (see exception below). Just wanted to bring
> >> >> > this to your attention.
> >> >> >
> >> >> > Traceback (most recent call last):
> >> >> >
> >> >> > File "./test_bpf.py", line 176, in <module>
> >> >> > sw_clock.open_perf_event(1, 0)
> >> >> >
> >> >> > File "/usr/lib/python2.7/dist-packages/bcc/table.py", line 410,
> in
> >> >> > open_perf_event
> >> >> > fd = self._open_perf_event(typ, config, i)
> >> >> > File "/usr/lib/python2.7/dist-packages/bcc/table.py", line 416,
> in
> >> >> > _open_perf_event
> >> >> > self[self.Key(cpu)] = self.Leaf(fd)
> >> >> > File "/usr/lib/python2.7/dist-packages/bcc/table.py", line 320,
> in
> >> >> > __setitem__
> >> >> > super(ArrayBase, self).__setitem__(key, leaf)
> >> >> > File "/usr/lib/python2.7/dist-packages/bcc/table.py", line 169,
> in
> >> >> > __setitem__
> >> >> > raise Exception("Could not update table")
> >> >> > Exception: Could not update table
> >> >> >
> >> >> > On Fri, Jul 29, 2016 at 1:34 PM, Brenden Blanco
> >> >> > <bbla...@plumgrid.com>
> >> >> > wrote:
> >> >> >> On Fri, Jul 29, 2016 at 10:21 AM, riya khanna
> >> >> >> <riyakhanna1...@gmail.com>
> >> >> >> wrote:
> >> >> >>>
> >> >> >>> I'm testing perf counters on a 8-core machine.
> >> >> >>>
> >> >> >>> since BPF_PERF_ARRAY.perf_read(cpu) reads from local CPU, I'm
> >> >> >>> aggregating counters across all cpus by doing:
> >> >> >>>
> >> >> >>> BPF_PERF_ARRAY(counter, 32);
> >> >> >>>
> >> >> >>> for (key = 0; key < 8; key++)
> >> >> >>> counter.perf_read(key);
> >> >> >>
> >> >> >>
> >> >> >> I think it would make more sense to only read the counter on the
> cpu
> >> >> >> where
> >> >> >> the event is taking place. So:
> >> >> >>
> >> >> >> u64 key = cycles.perf_read(bpf_get_smp_processor_id());
> >> >> >>
> >> >> >> And then aggregate counters in userspace.
> >> >> >>
> >> >> >> I have spent some time over the past couple days cleaning up the
> >> >> >> code
> >> >> >> in
> >> >> >> that private branch, but have been distracted a bit so haven't
> >> >> >> finalized it.
> >> >> >> Hopefully a PR will come soon.
> >> >> >>
> >> >> >>>
> >> >> >>> However, this reports error:
> >> >> >>>
> >> >> >>> bpf: Invalid argument
> >> >> >>> back-edge from insn 69 to 17
> >> >> >>>
> >> >> >>> If I loop from 0-4, it works. The code below works:
> >> >> >>> for (key = 0; key < 4; key++)
> >> >> >>> counter.perf_read(key);
> >> >> >>>
> >> >> >>>
> >> >> >>> What could be wrong here?
> >> >> >>
> >> >> >> The kernel verifier won't allow loops (i.e. back edges), and
> >> >> >> depending
> >> >> >> on
> >> >> >> the loop unroll optimization decision made by llvm, this short
> loop
> >> >> >> may
> >> >> >> have
> >> >> >> been automatically unrolled. Still, the solution should be to
> remove
> >> >> >> the
> >> >> >> loop and just read the local cpu's perf counter as mentioned
> above.
> >> >> >>>
> >> >> >>>
> >> >> >>>
> >> >> >>> On Tue, Jul 26, 2016 at 7:29 PM, riya khanna
> >> >> >>> <riyakhanna1...@gmail.com>
> >> >> >>> wrote:
> >> >> >>> > From your patches I see that perf support is enabled per-cpu.
> >> >> >>> > Could
> >> >> >>> > this be extended to enabling all or a group of perf counters on
> >> >> >>> > all
> >> >> >>> > CPU cores similar to what perf_event_open provides (with args
> >> >> >>> > -1)?
> >> >> >>> >
> >> >> >>> > On Mon, Jul 25, 2016 at 9:55 PM, riya khanna
> >> >> >>> > <riyakhanna1...@gmail.com>
> >> >> >>> > wrote:
> >> >> >>> >> Thanks Brenden!
> >> >> >>> >>
> >> >> >>> >> I will try with your changes. Meanwhile please let me know if
> >> >> >>> >> you
> >> >> >>> >> add
> >> >> >>> >> missing functionality.
> >> >> >>> >>
> >> >> >>> >>
> >> >> >>> >> On Mon, Jul 25, 2016 at 8:14 PM, Brenden Blanco
> >> >> >>> >> <bbla...@plumgrid.com>
> >> >> >>> >> wrote:
> >> >> >>> >>> This needs support in bcc.
> >> >> >>> >>>
> >> >> >>> >>> I had a patch laying around that I never finished, you can
> find
> >> >> >>> >>> the
> >> >> >>> >>> partial
> >> >> >>> >>> support here:
> >> >> >>> >>> https://github.com/iovisor/bcc/tree/perf-counter
> >> >> >>> >>>
> >> >> >>> >>> It shouldn't be too hard to finalize that, let me see what I
> >> >> >>> >>> can
> >> >> >>> >>> do.
> >> >> >>> >>>
> >> >> >>> >>> On Mon, Jul 25, 2016 at 4:11 PM, riya khanna via iovisor-dev
> >> >> >>> >>> <iovisor-dev@lists.iovisor.org> wrote:
> >> >> >>> >>>>
> >> >> >>> >>>> So I fixed the error above by using "count =
> >> >> >>> >>>> my_map.perf_read(key);"
> >> >> >>> >>>> as opposed to "count = bpf_perf_event_read(&my_map, key);".
> >> >> >>> >>>> However,
> >> >> >>> >>>> how do I selectively enable counters (e.g. instructions,
> cache
> >> >> >>> >>>> misses,
> >> >> >>> >>>> etc.)?
> >> >> >>> >>>>
> >> >> >>> >>>> Thanks,
> >> >> >>> >>>> Riya
> >> >> >>> >>>>
> >> >> >>> >>>> On Mon, Jul 25, 2016 at 9:58 AM, riya khanna
> >> >> >>> >>>> <riyakhanna1...@gmail.com>
> >> >> >>> >>>> wrote:
> >> >> >>> >>>> > Hi,
> >> >> >>> >>>> >
> >> >> >>> >>>> > I'm trying to read perf counters using bpf. However,
> adding
> >> >> >>> >>>> > BPF_PERF_ARRAY reports error:
> >> >> >>> >>>> >
> >> >> >>> >>>> > bpf: Invalid argument
> >> >> >>> >>>> > unrecognized bpf_ld_imm64 inns
> >> >> >>> >>>> >
> >> >> >>> >>>> > Is there an example/sample to read perf counters that I
> can
> >> >> >>> >>>> > follow?
> >> >> >>> >>>> > The code below is what I'm trying to execute.
> >> >> >>> >>>> >
> >> >> >>> >>>> > Thanks,
> >> >> >>> >>>> > Riya
> >> >> >>> >>>> >
> >> >> >>> >>>> > # load BPF program
> >> >> >>> >>>> >
> >> >> >>> >>>> > bpf_text = """
> >> >> >>> >>>> >
> >> >> >>> >>>> > #include <uapi/linux/ptrace.h>
> >> >> >>> >>>> >
> >> >> >>> >>>> > BPF_PERF_ARRAY(my_map, 32);
> >> >> >>> >>>> >
> >> >> >>> >>>> > int start_counting(struct pt_regs *ctx) {
> >> >> >>> >>>> >
> >> >> >>> >>>> > if (!PT_REGS_PARM1(ctx))
> >> >> >>> >>>> >
> >> >> >>> >>>> > return 0;
> >> >> >>> >>>> >
> >> >> >>> >>>> > u64 count;
> >> >> >>> >>>> >
> >> >> >>> >>>> > u32 key = bpf_get_smp_processor_id();
> >> >> >>> >>>> >
> >> >> >>> >>>> > count = bpf_perf_event_read(&my_map, key);
> >> >> >>> >>>> >
> >> >> >>> >>>> > bpf_trace_printk("CPU-%d %llu", key, count);
> >> >> >>> >>>> >
> >> >> >>> >>>> > return 0;
> >> >> >>> >>>> >
> >> >> >>> >>>> > }
> >> >> >>> >>>> >
> >> >> >>> >>>> > """
> >> >> >>> >>>> _______________________________________________
> >> >> >>> >>>> iovisor-dev mailing list
> >> >> >>> >>>> iovisor-dev@lists.iovisor.org
> >> >> >>> >>>> https://lists.iovisor.org/mailman/listinfo/iovisor-dev
> >> >> >>> >>>
> >> >> >>> >>>
> >> >> >>
> >> >> >>
> >> >
> >> >
> >
> >
>
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