Re: [PATCH RESEND 9/9] block, trace: implement ioblame - IO tracer with origin tracking

[Tejun Heo <tj@kernel.org>]

On Tue, Jan 10, 2012 at 05:32:12PM -0800, Tejun Heo wrote:
> Implement ioblame, which can attribute each IO to its origin and
> export the information using a tracepoint.
> 
> Operations which may eventually cause IOs and IO operations themselves
> are identified and tracked primarily by their stack traces along with
> the task and the target file (dev:ino:gen).  On each IO completion,
> ioblame knows why that specific IO happened and exports the
> information via ioblame:ioblame_io tracepoint.
> 
> While ioblame adds fields to a few fs and block layer objects, all
> logic is well insulated inside ioblame proper and all hooking goes
> through well defined tracepoints and doesn't add any significant
> maintenance overhead.
> 
> For details, please read Documentation/trace/ioblame.txt.
> 
> -v2: Namhyung pointed out that all the information available at IO
>      completion can be exported via tracepoint and letting userland do
>      whatever it wants to do with that would be better.  Stripped out
>      in-kernel statistics gathering.
> 
>      Now that everything is exported through tracepoint, iolog and
>      counters_pipe[_pipe] are unnecessary.  Removed.  intents_bin too
>      is removed.
> 
>      As data collection no longer requires polling, ioblame/intents is
>      updated to generate inotify IN_MODIFY event after a new intent is
>      created.

One planned update is exporting issuer and dirtier separately.
Currently dirtier, if exists, simply overrides issuer as it wasn't
useful for in-kernel statistics anyway.  With that gone, I think it
makes much more sense to expose both of them.

Thanks.

-- 
tejun