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SubjectRe: Benchmark results for elv_test (2.4.0-test9 and back).

Grab NWFS at vger.timpanogas.org. It has a really good ASYNCH I/O
abstraction in kernel that is pluggable and will allow very agressive
testing of the elevator code in 2.4.0. Check the file BLOCK.C for the
2.4 support and ASYNC.C. Theres a nice way to pump ons of AIO requests
into Linux with this interface, and it's fully asynch.

Jeff

"J. Robert von Behren" wrote:
>
> Greetings, Robert.
>
> Looking over your test program, I don't think you are actually testing
> the elevator algorithm at all. There are a couple of key flaws:
>
> * The reads and writes are synchronous, so the elevator algorithm
> at _most_ gets to effect the blocks within a single read or
> write (ie - inside the same file).
>
> * The fact that you have written the files out all at once will not
> place all 240 megs of data consecutively on the disk. The file
> system spreads out data on disk to allow breathing room for
> adding new files, or appending to existing files. In particular,
> this means that although large subsections of blocks that are
> adjacent in the logical file _will_ be close by on disk, you cannot
> generalize from this that these large subsections will be close to
> each other - either within a single file, or between the files
> created by the test program.
>
> * Unless the partition is completely empty, existing file data will
> effect where new data is placed (and in particular how well
> co-located
> it can be).
>
> A better approach to testing the elevator algorithm would be to write
> directly to a raw device, instead of going through the file system.
> This would allow you better control over actual disk placement of
> blocks, and let you know what you were testing. It would also allow you
> to make sure that subsequent re-tests would be repeatable, as they
> shouldn't be effected by existing data. Finally, to do this test right,
> you need to be able to issue multiple IO requests to the disk at
> essentially the same time. To do this, you'll probably need to go
> multithreaded, and use a barrier of some sort to make sure the threads
> stay synchronized.
>
> Best regards,
>
> -Rob von Behren
>
> Robert Cohen wrote:
> >
> > Here are the latest results for my elv_test elevator benchmark.
> > This benchmark gives three numbers, a baseline figure for writing
> > sequentially and write and read results for writing and reading in a
> > pattern designed to give the elevator a hard time.
> > The source code is available at
> > http://tltsu.anu.edu.au/~robert/elv_test.c.
> -
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