CmsIOInstrumenting < Main

---+ Instrumenting CMSSW I/O
This page discusses how to instrument CMSSW I/O at the Linux kernel in order to better understand how the application interacts with the block layer.  The goals are:
   1 Provide insights into how CMSSW (and hence ROOT) I/O's usage of various system calls results in disk activity.
   1 Identify potential performance bottlenecks.
   1 Experiment with potential solutions.

---+ Pages in this guide

!BlockTrace, a set of scripts to record and visualize Linux kernel I/O.
   1 [[Main.CmsIoBlockTrace][Using BlockTrace and !SystemTap on your system]].  How to run !BlockTrace on your systems in order to repeat the measurements I have made yourself.
   1 [[Main.CmsIoBlockTraceOutput][BlockTrace graphs]].  How to understand and read the !BlockTrace graphs I will be showing.
   1 [[Main.CmsIoSystemtap][User-level SystemTap tracing]].  Correlating between user-level events and kernel-level events.

Findings for CMSSW
   1 [[Main.CmsIoCmsswNocache][CMSSW with no cache]].  This is the out-of-the box behavior of CMSSW.
   1 [[Main.CmsIoCmsswApp][CMSSW with readHint=application-only]].  This turns on !TTreeCache, but does I/O in synchronous mode.
   1 [[Main.CmsIoCmsswStor][CMSSW with readHint=storage-only]].  This turns on !TTreeCache with I/O in asynchronous mode.
   1 [[Main.CmsIoCmssw2Cache][CMSSW with the 2-cache scheme]].  This turns on the 2-cache scheme, as described by Main.CmsIOWork2.

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
png	trace.png	r1	manage	49.1 K	2010-03-16 - 16:46	BrianBockelman

This topic: Main > TWikiUsers > BrianBockelman > CmsIOInstrumenting
Topic revision: r5 - 2010-05-13 - BrianBockelman