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    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 <> interface
    > 2. per-process IO statistics: None
    > Levent Serinol <> Needs are subset of CSA
    > 3. per-cpu time statistics: None (email bounced)
    > Erich Focht <> Needs can be met by taskstats
    > Statistics not yet submitted
    > 4. Microstate accounting: None
    > Peter Chubb <> overlap with delay accounting
    > prefers /proc due to
    > convenience
    > taskstats can meet the needs
    > 5. ELSA: Guillaume Thouvenin None
    > <> ELSA is not a direct user
    > of new kernel statistics
    > Consumer of CSA/BSD
    > accounting
    > statistics
    > 6. pnotify: Jes Sorensen <> 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 <>
    > 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
    > 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
    > (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.


    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.


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