Re: About the document of "blktrace" and "btt"

["Alan D. Brunelle" <Alan.Brunelle@hp.com>]

On Fri, 2010-03-05 at 15:01 +0800, leon wrote:
> Hi there,
> 
> Very appreciated about your "blktrace", "btt" and
> gelato_ICE06apr_blktrace_brunelle_hp.pdf. They are quite powerful!
> 
> I am using blktrace-1.0.1-4.3.i586 on kernel 2.6.31.8, but the btt
> output seems a little bit different from that pdf. This doc only
> explained Q2I I2D D2C Q2C 
> 
> Can anybody help to explain the detail meaning of:
> 
> Q2Q
> Q2G
> G2I
> Q2M
> M2D
> 
> Or is there any more detailed document about Q, G, I, M, D etc?
> 
> Thank you very much
> Leon

Hi Leon - 

Check out the btt.pdf generated by "make docs" - in a nutshell, 'Q'
traces indicates entry into the block I/O layer (more or less) so 'Q2Q'
would be the time between entries into the block I/O layer. 'G' is the
'request get' trace - so 'Q2G' shows the time needed to get a request.
'I' is the insert trace - so 'G2I' is how long it then took to find the
right queue spot to put the request on. 'M' is the merge trace - so
'Q2M' indicates how long it took to find & merge an incoming I/O, whilst
'M2D' indicates how long it took for that request to be 'issueD' - sent
down to the underlying device driver.

Regards,
Alan