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    DateTue, 06 Jun 2006 18:28:15 -0400
    FromShailabh Nagar <>
    SubjectRe: Merge of per task delay accounting (was Re: 2.6.18 -mm merge plans)
    Balbir Singh wrote:
    > Andrew Morton wrote:> >> per-task-delay-accounting-setup.patch>> per-task-delay-accounting-setup-fix-1.patch>> per-task-delay-accounting-setup-fix-2.patch>> per-task-delay-accounting-sync-block-i-o-and-swapin-delay-collection.patch
    >>>> per-task-delay-accounting-sync-block-i-o-and-swapin-delay-collection-fix-1.patch
    >>>> per-task-delay-accounting-cpu-delay-collection-via-schedstats.patch
    >> per-task-delay-accounting-cpu-delay-collection-via-schedstats-fix-1.patch
    >> per-task-delay-accounting-utilities-for-genetlink-usage.patch
    >> per-task-delay-accounting-taskstats-interface.patch
    >> per-task-delay-accounting-taskstats-interface-fix-1.patch
    >> per-task-delay-accounting-taskstats-interface-fix-2.patch
    >> per-task-delay-accounting-delay-accounting-usage-of-taskstats-interface.patch
    >>>> per-task-delay-accounting-delay-accounting-usage-of-taskstats-interface-use-portable-cputime-api-in-__delayacct_add_tsk.patch
    >>>> per-task-delay-accounting-documentation.patch>> per-task-delay-accounting-proc-export-of-aggregated-block-i-o-delays.patch
    >>>> per-task-delay-accounting-proc-export-of-aggregated-block-i-o-delays-warning-fix.patch
    >>>>>>  I just don't know.  There are a number of groups who pop up with various
    >>  enhanced accounting requirements and patches (all quite different) but I
    >>  haven't heard a lot of enthusiasm from any of them over this work, which
    >>  attempts to provide an extensible framework for accumulation and
    >> querying
    >>  of per-task metrics.
    >>
    >>  But then again, we cannot just sit there and wait for everyone to be
    >> 100%
    >>  happy.  So I'm 51% inclined to push this along.
    >>
    >>  Anyone else who has an interest in this sort of thing needs to be aware
    >>  that there will be an expectation that any future statistics submissions
    >>  should use these interfaces.  So the time to pay attention is right now.
    >>> > Hi, Andrew,> > Here is a brief summary of the status of the response we have received from
    > the stakeholders (some of it has been duplicated in previous postings)
    > > Project                                         Response
    > > 1. CSA accounting/PAGG/JOB:                    Has agreed to use taskstats
    >  Jay Lan <jlan@engr.sgi.com>                  interface
    > 
    > 2. per-process IO statistics:                  None
    >  Levent Serinol <lserinol@gmail.com>          Needs are subset of CSA
    > 
    > 3. per-cpu time statistics:                    None (email bounced)
    >  Erich Focht <efocht@ess.nec.de>              Needs can be met by taskstats
    >                                               Statistics not yet submitted
    > 
    > 4. Microstate accounting:                      None
    >  Peter Chubb <peterc@gelato.unsw.edu.au>      overlap with delay accounting
    >                                               prefers /proc due to
    > convenience
    >                                               taskstats can meet the needs
    > 
    > 
    > 5. ELSA: Guillaume Thouvenin                   None
    >  <guillaume.thouvenin@bull.net>               ELSA is not a direct user
    >                                               of new kernel statistics
    >                                               Consumer of CSA/BSD
    > accounting
    >                                               statistics
    > 
    > 6. pnotify: Jes Sorensen <jes@sgi.com>         None
    > (taken over pnotify from Erik Jacobson)        Informed over private email
    >                                               that pnotify replacement is
    >                                               being worked on. pnotify
    >                                               or its replacement will
    >                                               not be concerned with
    >                                               exporting data to user space
    >                                               or collecting any statistics.
    > 
    > 
    > 7. Scalable statistics counters with /proc      Not working on it
    >  reporting:                                   anymore
    >  Ravikiran G Thirumalai,
    >  Dipankar Sarma <dipankar@in.ibm.com>
    > 
    > Studying the responses from all stake holders, Jay Lan's was the most
    > encouraging. Peter Chubb prefers the /proc interface due to the text
    > interface
    > and ease of parsing. (in our opinion, taskstats can meet the needs easily
    > and the getdelays utility can provide the same ease for parsing).
    > The others did not respond.
    > Some performance numbers of taskstats were posted at
    > http://lkml.org/lkml/2006/3/23/141. The result highlights are included
    > below
    > 
    >    Results highlights
    > 
    >    - Configuring delay accounting adds < 0.5%
    >      overhead in most cases and even reduces overhead
    >      in some cases
    > 
    >    - Enabling delay accounting has similar results
    >      with a maximum overhead of 1.2% for hackbench,
    >      most other overheads < 1% and reduction in
    >      overhead in some cases
    > 
    > These statistics are _per task_ and can be extended easily by anyone
    > who wishes to obtain per task data. An example of per task improved
    > scheduler statistics was mentioned in http://lkml.org/lkml/2006/6/1/381
    > (I am not sure if the email refers to our per-task statistics). If not,
    > the new statistics could easily use the taskstats interface.
    > 
    > These statistics can be used by software product stacks to monitor
    > usage information about the various tasks they create and control.
    > I also informally spoke to a group of students (verbally), who were
    > excited at the possibility of using the per-task statistics to do
    > dynamic deadline based power management. They want to use the delay data
    > (CPU and IO) to predict deadlines for a task and then use these results
    > for dynamically scaling CPU frequency.
    > 
    > 
    > The ability to monitor the CPU run and delay data and IO delay data is
    > useful.
    > 
    > I would request you to consider the inclusion per-task delay accounting
    > into
    > 2.6.18.
    > 
    
    
    Andrew,
    
    The only other new set of patches to be discussed in this context are the
    statistics-infrastructure patches from Martin Peschke.
    
    That infrastructure cannot meet the needs of delay accounting, CSA etc. because
    - it only provides "user pull" model of getting stats whereas "kernel push" is
    needed for delay accounting
    - it uses a relatively slow interface unsuitable for high volumes of data. Each
    statistic has its own definition, needs to be read separately using ASCII,
    reading data continuously means open/read/close each time.....all of
    which is not very conducive to large structures being sent to userspace.
    - its oriented towards sampled data whereas taskstats isn't.
    So, we have a good consensus from existing/potential users of taskstats and would
    very much appreciate it being included in 2.6.18.
    
    --Shailabh
    
    
    
    
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