Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 05, 2016 at 12:45:07PM -0700, Alexei Starovoitov wrote: > Also thinking about concurrency and the need to remember the original > handler somewhere, would it be cleaner api to add a bit to perf_event_attr > and use attr.config1 as bpf_fd ? attr.config[12] are in use already,

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 05, 2016 at 12:45:07PM -0700, Alexei Starovoitov wrote: > Also thinking about concurrency and the need to remember the original > handler somewhere, would it be cleaner api to add a bit to perf_event_attr > and use attr.config1 as bpf_fd ? attr.config[12] are in use already,

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 05, 2016 at 10:22:08AM -0700, Brendan Gregg wrote: > (Normally I'd use I$ miss overflow, but none of our Linux systems have > PMCs: cloud.) I think I had better not comment on that ;-) > >> > The perf:perf_hrtimer probe point is also reading state mid-way > >> > through a function,

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 05, 2016 at 10:22:08AM -0700, Brendan Gregg wrote: > (Normally I'd use I$ miss overflow, but none of our Linux systems have > PMCs: cloud.) I think I had better not comment on that ;-) > >> > The perf:perf_hrtimer probe point is also reading state mid-way > >> > through a function,

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 05, 2016 at 12:52:09PM +0200, Peter Zijlstra wrote: > > > > Currently overflow_handler is set at event alloc time. If we start > > > > changing it on the fly with atomic xchg(), afaik things shouldn't > > > > break, since each overflow_handler is run to completion and doesn't > > > >

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 05, 2016 at 12:52:09PM +0200, Peter Zijlstra wrote: > > > > Currently overflow_handler is set at event alloc time. If we start > > > > changing it on the fly with atomic xchg(), afaik things shouldn't > > > > break, since each overflow_handler is run to completion and doesn't > > > >

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 5, 2016 at 3:52 AM, Peter Zijlstra wrote: > On Thu, Aug 04, 2016 at 10:24:06PM -0700, Alexei Starovoitov wrote: >> tracepoints are actually zero overhead already via static-key mechanism. >> I don't think Peter's objection for the tracepoint was due to overhead.

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Fri, Aug 5, 2016 at 3:52 AM, Peter Zijlstra wrote: > On Thu, Aug 04, 2016 at 10:24:06PM -0700, Alexei Starovoitov wrote: >> tracepoints are actually zero overhead already via static-key mechanism. >> I don't think Peter's objection for the tracepoint was due to overhead. > > Almost 0, they

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 04, 2016 at 10:24:06PM -0700, Alexei Starovoitov wrote: > tracepoints are actually zero overhead already via static-key mechanism. > I don't think Peter's objection for the tracepoint was due to overhead. Almost 0, they still have some I$ footprint, but yes. My main worry is that we

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 04, 2016 at 10:24:06PM -0700, Alexei Starovoitov wrote: > tracepoints are actually zero overhead already via static-key mechanism. > I don't think Peter's objection for the tracepoint was due to overhead. Almost 0, they still have some I$ footprint, but yes. My main worry is that we

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 04, 2016 at 09:13:16PM -0700, Brendan Gregg wrote: > On Thu, Aug 4, 2016 at 6:43 PM, Alexei Starovoitov > wrote: > > On Thu, Aug 04, 2016 at 04:28:53PM +0200, Peter Zijlstra wrote: > >> On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: > >> >

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 04, 2016 at 09:13:16PM -0700, Brendan Gregg wrote: > On Thu, Aug 4, 2016 at 6:43 PM, Alexei Starovoitov > wrote: > > On Thu, Aug 04, 2016 at 04:28:53PM +0200, Peter Zijlstra wrote: > >> On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: > >> > >> > As for pmu tracepoints:

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 4, 2016 at 6:43 PM, Alexei Starovoitov wrote: > On Thu, Aug 04, 2016 at 04:28:53PM +0200, Peter Zijlstra wrote: >> On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: >> >> > As for pmu tracepoints: if I were to instrument it (although I wasn't

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 4, 2016 at 6:43 PM, Alexei Starovoitov wrote: > On Thu, Aug 04, 2016 at 04:28:53PM +0200, Peter Zijlstra wrote: >> On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: >> >> > As for pmu tracepoints: if I were to instrument it (although I wasn't >> > planning to), I'd put a

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 04, 2016 at 04:28:53PM +0200, Peter Zijlstra wrote: > On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: > > > As for pmu tracepoints: if I were to instrument it (although I wasn't > > planning to), I'd put a tracepoint in perf_event_overflow() called > >

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Thu, Aug 04, 2016 at 04:28:53PM +0200, Peter Zijlstra wrote: > On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: > > > As for pmu tracepoints: if I were to instrument it (although I wasn't > > planning to), I'd put a tracepoint in perf_event_overflow() called > >

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: > As for pmu tracepoints: if I were to instrument it (although I wasn't > planning to), I'd put a tracepoint in perf_event_overflow() called > "perf:perf_overflow", with the same arguments. That could then be used > for all PMU

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 03, 2016 at 11:57:05AM -0700, Brendan Gregg wrote: > As for pmu tracepoints: if I were to instrument it (although I wasn't > planning to), I'd put a tracepoint in perf_event_overflow() called > "perf:perf_overflow", with the same arguments. That could then be used > for all PMU

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 3, 2016 at 2:48 AM, Peter Zijlstra wrote: > > On Wed, Aug 03, 2016 at 02:47:47AM +, Brendan Gregg wrote: > > When perf is performing hrtimer-based sampling, this tracepoint can be used > > by BPF to run additional logic on each sample. For example, BPF can

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 3, 2016 at 2:48 AM, Peter Zijlstra wrote: > > On Wed, Aug 03, 2016 at 02:47:47AM +, Brendan Gregg wrote: > > When perf is performing hrtimer-based sampling, this tracepoint can be used > > by BPF to run additional logic on each sample. For example, BPF can fetch > > stack traces

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 03, 2016 at 02:47:47AM +, Brendan Gregg wrote: > When perf is performing hrtimer-based sampling, this tracepoint can be used > by BPF to run additional logic on each sample. For example, BPF can fetch > stack traces and frequency count them in kernel context, for an efficient >

Re: [PATCH v2 1/3] perf/core: Add a tracepoint for perf sampling

On Wed, Aug 03, 2016 at 02:47:47AM +, Brendan Gregg wrote: > When perf is performing hrtimer-based sampling, this tracepoint can be used > by BPF to run additional logic on each sample. For example, BPF can fetch > stack traces and frequency count them in kernel context, for an efficient >