Re: [PATCH] sched: Provide iowait counters

[Arjan van de Ven]

Andrew Morton wrote:
> On Fri, 24 Jul 2009 21:33:02 -0700 Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> wrote:
>
> > Andrew Morton wrote:
> > > On Mon, 20 Jul 2009 11:31:47 -0700 Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> wrote:
> > >
> > > > For counting how long an application has been waiting for (disk) IO,
> > > > there currently is only the HZ sample driven information available, while
> > > > for all other counters in this class, a high resolution version is
> > > > available via CONFIG_SCHEDSTATS.
> > > >
> > > > In order to make an improved bootchart tool possible, we also need
> > > > a higher resolution version of the iowait time.
> > > >
> > > > This patch below adds this scheduler statistic to the kernel.
> > > Doesn't this duplicate the delay accounting already available via the
> > > taskstats interface?
> > we have how long we wait. we do not have how long we iowait afaik...
> > at least not in nanosecond granularity. (We do have the sampled data, but that
> > is milisecond sampled data, not very useful for making charts based on time
> > to show the sequence of events)
>
> See include/linux/sched.h's definition of task_delay_info - u64
> blkio_delay is in nanoseconds.  It uses
> do_posix_clock_monotonic_gettime() internally.

looks like it does.. to bad we don't expose that data in a /proc/<pid>/delay or something field
like we do with the scheduler info...


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