On 03/26/2018 06:51 PM, Steven Rostedt wrote:
> On Sat, 24 Mar 2018 17:26:38 +0100
> Matthias Schiffer <mschif...@universe-factory.net> wrote:
>
>> @@ -905,8 +898,20 @@ static void profile_graph_return(struct
>> ftrace_graph_ret *trace)
>>
>> rec = ftrace_find_profiled_func(stat, trace->func);
>> if (rec) {
>> + unsigned long long avg, delta1, delta2;
>> +
>> rec->time += calltime;
>> - rec->time_squared += calltime * calltime;
>> +
>> + /* Apply Welford's method */
>> + delta1 = calltime - rec->avg;
>> +
>> + avg = rec->time;
>> + do_div(avg, rec->counter);
>
> Can you find a way not to do a divide in every function call?I think the current method based on the sum of squares is the best we can do without a divide for each sample. The completely bogus result nf_conntrack_proto_fini 50 373.523 us 7.470 us 3234315951 us I mentioned in my commit message was caused by the second MIPS-specific issue I mentioned in my last mail, so while this method may lead to inaccurate results [1], and it is certainly not Welford's method, it might be good enough in practice, and you can disregard my patch. Matthias [1] http://jonisalonen.com/2013/deriving-welfords-method-for-computing-variance/ > > -- Steve > >> + rec->avg = avg; >> + >> + delta2 = calltime - rec->avg; >> + >> + rec->stddev += delta1 * delta2; >> } >> >> out: >
signature.asc
Description: OpenPGP digital signature
