Messages in this thread | | | Date | Thu, 25 Nov 2010 14:22:51 +0100 | Subject | Re: [RFC PATCHv3] perf tools: add event grouping capability to "perf stat" | From | Stephane Eranian <> |
| |
On Thu, Nov 25, 2010 at 2:19 PM, Stephane Eranian <eranian@google.com> wrote: > On Thu, Nov 25, 2010 at 7:32 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: >> On Wed, 2010-11-24 at 17:54 -0800, Corey Ashford wrote: >>> Add the ability to create multiple event groups, each with their own leader >>> using the existing "-e <event>[,<event> ...] [-e <event>[,<event>]]" >>> syntax. Each additional -e switch creates a new group, and each event >>> listed within a -e switch is within that group. >>> >>> Changes since v1: >>> - Because of a flub, v2 did not contain the changes I had intended to make, >>> and instead, v2 had the same patch contents as v1. >>> - When perf stat is not supplied any events on the command line, put >>> each default event in its own group. >> >> I like this, but could you also extend this to perf-record? its a bit >> odd to diverge between the two. >> >> Using Stephane's latest syntax changes you could actually do something >> like: >> >> perf record -e task-clock:freq=1000,cycles:period=0 >> >> Which would create a group with 1 sampling counter and a counting >> counter (at which point we should probably start flipping >> PERF_SAMPLE_READ). >> > > I think using PERF_SAMPLE_READ may expose a problem in the > perf.data format. To correctly parse a sample created with SAMPLE_READ, > you need to know the attr.read_format. But for that you need to know the > event which caused the sample, but for that you need the SAMPLE_ID, > and you don't know if it's there or not. In other words, there is a chicken > and egg problem. > > I think the issue is that PERF_RECORD_SAMPLE is missing a mandatory > piece of information: overflow event ID. This must a mandatory field, not > optional as it is today. It is okay when you have only one group, but we'd > like to go beyond that. > Second thought on this, I think the problem is in the kernel and not so much in the perf.data file. Kernel must provide enough information to correlate samples to events. It must do in a way that is not optional. Otherwise, as soon as you have multiple groups, you won't be able to parse SAMPLE_READ. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |