[599] in Info-AFS_Redistribution
Re: NFS vs. AFS builds
daemon@ATHENA.MIT.EDU (Sven Tafvelin)
Wed Feb 12 03:31:33 1992
Date: Wed, 12 Feb 92 07:46:27 GMT
From: Sven Tafvelin <tafvelin@ce.chalmers.se>
To: dstokes@sunlight.austin.ibm.com, ed@pa.dec.com
Cc: carl@shade.austin.ibm.com, info-afs@transarc.com
Craig Andersson writes:
>> AFS is slower to do builds. A lot slower. Why is this? Why doesn't
>> a 200MB cache fix this? Why is the 2nd build no faster than the first?
The reason may be that the build needs more than 200 Mbytes of files which
means that it will remove the files soon needed when restarting the
build.
Ed Gould writes:
>> Tha answer is almost certainly that AFS synchronizes its writes to the server at
>> file close time, waiting for the entire file to be written to the server at that
>> time. NFS is synchronous to the server on a block-by-block basis, hence it
>> doesn't wait for the writes to complete at any point - blocks are flushed to the
>> server as required by the client buffer cache. This typically happens in parallel
>> to other activity.
This can only be part of the explanation. It doesn't explain why so much
system CPU time is used. I think the system CPU time consumption is the
key clue to the problem, but I cannot explain it. Look at the tables given
by Craig Andersson:
>> Real User Sys Comments
>> AFS 1st time 7:54.13 2:42.61 3:49.02 ~82% CPU utilizaton
>> 2nd time ** 7:54.49 2:42.77 3:48.24 ~82% CPU utilizaton
>> NFS 1st time 4:15.01 2:15.38 25.71 ~64% CPU utilizaton
>> 2nd time 4:04.51 2:15.29 26.31 ~66% CPU utilizaton
>> Below is a comparison on non-compile build performance (target is up to date).
>> Time for lm to determine "Target rsdd is up to date.". This is similar
>> to the time from execution of "lm" command to start of first compile
>> (AFS is much much slower here). AFS took about 4.5 longer than NFS
>> (and consumed about 8 times more CPU time):
>> Real User Sys Comments
>> AFS ** 3:54.14 18.78 3:13.05 ~91% CPU utilizaton
>> AFS ** 3:44.72 18.99 3:12.77 ~95% CPU utilizaton
>> NFS 49.40 10.85 14.69 ~51% CPU utilizaton
>> NFS 46.73 10.73 14.94 ~55% CPU utilizaton
Regards
Sven Tafvelin
