This is the mail archive of the mailing list for the systemtap project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

RE: Tune reader_thread poll timeout value

>I agree with Frank that it would be nicer to have one "tunable" instead
>of two
Good that you seem OK with introduction of a tunable. I was not sure about correlating s and ns values, I will follow the suggestion of a MS tunable to derive s and ns values.

> Also don't forget to add some small documentation to stap.1
>describing the default value and implications of tuning it higher/lower.
+ comment from Frank Eigler
>Do you notice any adverse effects from this?  For an output-heavy script for example, does this cause more out-of-buffer conditions?

Several remarks:
- OK for doc. There is a section with MAXNESTING, MAXSTRINGLEN, ... Is it the right place ? It seems it is more related to module itself (like STP_RELAY_TIMER_INTERVAL and STP_CTL_TIMER_INTERVAL that we also use)

- My understanding is that reader_thread ppoll should return (value > 0) on production of a relayfs subbuffer. If timing out, we read an "uncomplete" buffer. So, in case of output-heavy script, we should simply not time-out so tunable should not have any adverse effect.

We keep using 5s tunable and observe (without checking ppoll returned for sub-buffer or timeout):
   * not output-heavy script: waiting 5s before having "probe begin" trace ;-) It seems to print something every k*5 s but script is not producing regularly so I will double check with "probe timer.s(2)" + single trace script to observe behaviour
   * a bit more output-heavy script (scheduler contextswitch, irqs, workqueues, freq changes): I see stapio waking up between 1 to 3s so I imagine ppoll does not return on timeout but on subbuffer production. Everything goes well. I have 1 colleague who checked when systemtap was breaking due to trace bandwidth, I will make him use 2 versions of staprun.

And then submit final patch to review


Texas Instruments France SA, 821 Avenue Jack Kilby, 06270 Villeneuve Loubet. 036 420 040 R.C.S Antibes. Capital de EUR 753.920

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]