Messages in this thread | | | Subject | Re: [patch 0/4] perf_counter tools: support annotation of live kernel modules | From | Mike Galbraith <> | Date | Fri, 03 Jul 2009 09:36:25 +0200 |
| |
On Fri, 2009-07-03 at 09:27 +0200, Ingo Molnar wrote: > * Mike Galbraith <efault@gmx.de> wrote: > > > On Thu, 2009-07-02 at 09:42 +0200, Ingo Molnar wrote: > > > > (squirrels suggestions away for later reference) > > > > > Btw, another thing: we are thinking about making -F 1000 (1 KHz > > > auto-freq sampling) the default for perf top and perf record. This > > > way we'd always gather enough data (and never too much or too little > > > data), regardless of the intensity of the workload. Have you played > > > with -F before, what's your general experience about it? It's > > > particularly useful for 'rare' and highly fluctuating events like > > > cache-misses. > > > > > > Maybe 1KHz is a bit too low - Oprofile defaults to 100000 cycles > > > interval by default which is about 10 KHz on a 1GHz box and 30 > > > KHz on a 3GHz box. Perhaps 10 KHz is a better default? > > > > My default usage is 1000Hz to keep overhead low. Works fine for > > me. > > ah, so you use -F by default?
Yes.
> I still think 10 KHz would be better - especially for really short > runs like 'perf record -f -g ./git gc'. Since Oprofile samples at 26 > KHz by default, we must not go to a too low frequency, otherwise > people might get a 'hm, the perf profiles are worse than the > Oprofile ones' first impression ... > > We could perhaps add a freq=1000 switch to .perfconfig - we have > Git's util/config.c facility - it's just unused right now ;-) > > [ Look at the Git sources about how config.c is used. ]
Yeah, that's a good idea.. everyone can roll their own defaults.
For me, it doesn't matter what the default is, I always specify.
-Mike
| |