[Disksim-users] Request coalescence

[mingju Li]

We found that the program would stop when it has the number of requests the
user asks for in the generating list which means some requests are still in
the queues in different places like in controller or disks waiting for the
service. So you will find in the result that "total number of requests
generated" is the number of requests you asked for but "the total number of
requests handled" is always less than "the total number of requests
generated".  Although I tested it using synchronous way but I think it
should work the same way with using trace.

Ming

On 5/13/07, Greg Ganger <ganger at ece.cmu.edu> wrote:
>
>
> Cache hits would cause the number of requests at the disk to be less
> than the number in the trace.  That's something to look at.
>
> Greg
>
>
> On Sun, 13 May 2007, YipKei Kwok wrote:
>
> > Hi,
> >
> > I am running Disksim w./ a trace workload.
> >
> > Problem:
> > The amount of "Total Requests handled" by the disk is less than the
> > number of requests specified in the trace.
> >
> > I suspect that is because of request coalescence/overlapping/combining.
> >
> > disksim_ioqueue: Overlapping request scheme
> > -----------------------------------------------------------
> > - We have already set this parameter 0 so that overlapping requests
> > are treated as independent.
> >
> > disksim_disk: Combine seq writes
> > -------------------------------------------
> > - The default value of our HP C3323 hard drive is 1. We experienced
> > _exactly_ the same problem even when we set it to 0.
> >
> > I/O Driver Statistics
> > -------------------------
> >> From the statistics, both "IOdriver Overlaps combined" and "IOdriver
> > Read overlaps combined" are both 0. So, no requests are combined on
> > the I/O driver level.
> >
> >
> > Is there any other level of the I/O hierarchy could cause request
> > coalescence? Or, are there some other reasons, other than request
> > coalescence, which cause the problem that I am facing?
> >
> > Thank you very much!
> >
> > -Yipkei
> >
> > P.S. Here is our experimental setup.
> > I/O trace-driven
> > raid 0 - 1 HP C3323A hard drive.
> > (Originally, there are 4 disks in the RAID. For simplicity, now we
> > only use 1. So, strictly speaking, it's not a RAID.
> > Number of processors = 1
> >
> > --
> > Web site:
> > http://360.yahoo.com/yipkeikwok
> > http://www.mcs.csueastbay.edu/~ykwok/<http://www.mcs.csueastbay.edu/%7Eykwok/>
> > email addresses:
> > yipkeikwok at gmail dot com
> > ykwok2 at utep dot edu
> > ICQ UIN:    2309842
> > Google Talk ID:    yipkeikwok at gmail dot com
> > Yahoo! Messenger ID:    yipkeikwok
> > MSN Messenger ID:    yipkeikwok at hotmail dot com
> > _______________________________________________
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> >
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