Re: [PATCH] sched: Provide iowait counters

[Arjan van de Ven <arjan@linux.intel.com>]

Andrew Morton wrote:
> On Fri, 24 Jul 2009 21:33:02 -0700 Arjan van de Ven <arjan@linux.intel.com> wrote:
> 
>> Andrew Morton wrote:
>>> On Mon, 20 Jul 2009 11:31:47 -0700 Arjan van de Ven <arjan@linux.intel.com> 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...