Re: [RFC] Implement simple messages in blktrace stream

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, May 23 2008, Alan D. Brunelle wrote:
> The following two patches (kernel + application) would allow one to
> annotate parts of the blktrace stream w/ simple messages.
> 
> I've included a sample one for elevator switches:
> 
>   8,16   1   813055    20.259000000  4692  I   R 3088320 + 8 [dd]
>   8,16   1   813056    20.259000000  4692  Q   R 3088328 + 8 [dd]
>   8,16   1             20.259000000     0  m   N elv switch: deadline
>   8,16   1   813057    20.259000000  4692  G   R 3088328 + 8 [dd]
>   8,16   1   813058    20.259000000  4692  I   R 3088328 + 8 [dd]
> 
> These patches are a bit rough (but compile, and appear to work ok so
> far). In particular, I'd break the kernel patch into a blktrace addition
> and an elevator switch addition, plus the application patch would need
> documentation updates.
> 
> My nefarious ultimate goal would be to add in the ability for user-level
> insertions for (e.g.):
> 
> 1. Start blktrace
> 2. Do some stuff...
> 3. Insert a tag "switching to other stuff"
> 4. Do other stuff
> 5. Insert a tag "switching to yet other stuff"
> 6. Do yet other stuff
> 
> This way you could study different parts of the resultant traces using
> the tags to separate them time-wise. [For now, I'd just switch
> schedulers back and forth to see the separators.)
> 
> Looking for comments (hence the RFC).

Great stuff, I've done custom trace events and processing before so it's
really nice to have it generalized here. Thanks Alan!

-- 
Jens Axboe