[PVFS-developers] "Parallelizing" manager cross-talk to IODs

[Rob Ross]

Hi,

Applied in CVS.

Thanks!

Rob

On Wed, 28 Apr 2004, White Stuart - stwhit wrote:

> Hello all,
> 
> The pvfs manager frequently sends requests to each of the IODs in order to
> process requests.  It calls send_req() to accomplish this.  The send_req()
> routine contains a loop that loops through all the IODs, sending the request
> and waiting for the ACK from the IOD.  To illustrate:
> 
> forall (IODs)
> {
>    send_request_to_IOD();
>    wait_for_ACK();
> }
> 
> What results from this is that the IOD requests are sent in a very
> sequential manner; the manager waits for an ACK from an IOD before sending
> the request to the next IOD.  In general, this is acceptable.  However, in
> cases where the IOD takes a significant amount of time to service the
> request, this method of sending requests to the IODs is inefficient.  The
> time it takes for the manager to service the request is the sum of the times
> it takes for the IODs to service their requests.
> 
> I would like to suggest that we restructure the code to look like this:
> 
> forall (IODs)
> {
>    send_request_to_IOD();
> }
> 
> forall (IODs)
> {
>    wait_for_ACK();
> }
> 
> This effectively "parallelizes" the requests to the IODs.  Now, the time it
> takes the manager to service the request is only equal to the longest time
> one IOD takes to service its request.
> 
> I've attached a patch against the 1.6.2 source tarball that implements this
> change.
> 
> I ask that the PVFS developers take a look at this suggestion and see if it
> makes sense to them.  This change *seems* to make sense to me, but perhaps
> I'm overlooking something.  All feedback is greatly appreciated!
> 
> Stuart
> 
> 
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