* Alan D. Brunelle <Alan.Brunelle@xxxxxx> wrote: > o All kernels start off with Linux 2.6.23-rc6 + 2.6.23-rc6-mm1 > > o '- bt cfg' or '+ bt cfg' means a kernel without or with blktrace > configured respectively. > > o '- markers' or '+ markers' means a kernel without or with the > 11-patch marker series respectively. > > 38 runs without blk traces being captured (dropped hi/lo value from 40 runs) > > Kernel Options Min val Avg val Max val Std Dev > ------------------ --------- --------- --------- --------- > - markers - bt cfg 15.349127 16.169459 16.372980 0.184417 > + markers - bt cfg 15.280382 16.202398 16.409257 0.191861 > > - markers + bt cfg 14.464366 14.754347 16.052306 0.463665 > + markers + bt cfg 14.421765 14.644406 15.690871 0.233885 actually, the pure marker overhead seems to be a regression: > - markers - bt cfg 15.349127 16.169459 16.372980 0.184417 > + markers - bt cfg 15.280382 16.202398 16.409257 0.191861 why isnt the marker near zero-cost as it should be? (as long as they are enabled but are not in actual use) 2% increase is _ALOT_. That's the whole point of good probes: they do not slow down the normal kernel. _Worst case_ it should be at most a few instructions overhead but that does not explain the ~2% wall-clock time regression you measured here. So there's something wrong going on - either markers have unacceptably high cost, or the measurement is not valid. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-btrace" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
