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SubjectRe: performance of filesystem xattrs with Samba4
tridge@samba.org wrote:

>Hans,
>
> > can you describe qualitatively what your test does?
>
>The access patterns are very similar to dbench, which I believe you
>are already familiar with. Let me know if you'd like an explanation of
>dbench.
>
>
Actually, I would, because I have never read its code, and have been at
a loss for years to understand its meaning as a result of that.

>For the test I ran, the basic load file is almost the same as dbench,
>but the interpretation of the load file is a little bit different.
>
>For example, when the load file says "open a file", Samba4 needs to
>first stat() the file, and if xattrs are being used then it needs to
>do a fgetattr() to grab the extended DOS attributes. Additionally, if
>the open has the effect of changing any of those attributes then
>Samba4 needs to use fsetxattr() to write back the extended attributes,
>and sometimes fchmod() and utime() as well depending on the open
>parameters.
>
>When dbench interprets one of these load files it would just call
>open(), skipping all the extra system calls.
>
>The full load file I used is at:
>
> http://samba.org/ftp/tridge/dbench/client_enterprise.txt
>
>and is based on a capture of a "Enterprise Disk Mix" Netbench run,
>captured using the "nbench" load capturing proxy module in Samba4,
>using a Win2003 server backend and WinXP client.
>
>The working set size is approximately 20 MByte per client, and I was
>testing with 10 simulated clients. That means its very much a "in
>memory" test, as the machine has 2G of ram.
>
>
Ah, that explains a lot. For that kind of workload, the simpler the fs
the better, because really all you are doing is adding overhead to
copy_to_user and copy_from_user. All of reiser4's advanced features
will add little or no value if you are staying in ram.

> > You didn't answer whether it does fsyncs, etc.
>
>I think I did mention that the test does no fsync calls in the
>configuration I used. The reason I qualify the answer is that the load
>file actually contains approximately 1% Flush calls, but in its
>default configuration these are noops for Samba4. This is due to the
>confusion in Win32 between a "flush" operation and a "fsync"
>operation. Microsoft programmers use "flush" like a unix programmer
>would use fflush() on stdio, which is a noop for Samba. You can also
>configure Samba to treat flush as a "fsync", which is quite a
>different operation.
>
>The operation mix is as follows, listed with the approximate posix
>equivalent operation.
>
>(27%) ReadX (==pread)
>(17%) NTCreateX (==open)
>(16%) QUERY_PATH_INFORMATION (==stat)
>(13%) Close (==close)
>(9%) WriteX (==pwrite)
>(6%) FIND_FIRST (==opendir/readdir/closedir)
>(3%) Unlink (==unlink)
>(3%) QUERY_FS_INFORMATION (==statfs)
>(3%) QUERY_FILE_INFORMATION (==fstat)
>(1%) SET_FILE_INFORMATION (==fchmod/utime)
>(1%) Flush (==noop)
>(1%) Rename (==rename)
>(0%) UnlockX (==fcntl unlock)
>(0%) LockX (==fcntl lock)
>
>but the above can be a little misleading, as (for example) NTCreateX
>is a very complex call, and can be used to create directories, create
>files, open files or even delete files or directories (using the
>delete on close semantics).
>
> > It might be worth testing it with the extents only mount option for
> > reiser4.
>
>My apologies if I have just missed it, but I can't see an option that
>looks like "extents only" in either reiser4_parse_options() or in
>Documentation/filesystems/reiser4.txt in 2.6.10-rc2-mm2. Can you let
>me know the exact option name?
>
>Cheers, Tridge
>
>
>
>
mkfs.reiser4 -o extent=extent40
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