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    SubjectRe: [performance bug] kernel building regression on 64 LCPUs machine
    On Tue 22-03-11 13:46:06, Jeff Moyer wrote:
    > Jan Kara <jack@suse.cz> writes:
    >
    > > Jeff, I suppose the log files of fs_mark processes are on the same
    > > device as the test directory, aren't they - that might explain the
    > > flusher thread doing IO? The patch below
    >
    > No. My test environments are sane. The file system is on a completely
    > separate disk and it is unmounted and remounted in between each run.
    > That should take care of any lost flushes.
    OK, I understand but let me clear out one thing. What fs_mark seems to be
    doing is:
    for given number of iterations { (-L option, default 1)
    fork each thread {
    start timer
    for i = 1 .. 10000 { (could be changed by option -n)
    write file i
    }
    stop timer
    for i = 1 .. 10000 {
    unlink file i
    }
    write statistics to log file
    exit
    }
    read all log files, write combined results to another log file
    }

    I see from blktrace data that indeed you are running more than one
    iteration of the fs_mark process so the problem I was wondering about is
    whether unlinking or writing of log files cannot interefere with the IO
    happening while the timer is running.

    Now log files are rather small so I don't really think they cause any
    problem but they could be the data flusher thread writes - they are stored
    in the current directory (unless you use -l option). So I my question was
    aiming at where these files are stored - do you specify -l option and if
    not, what is the current directory of fs_mark process in your setup?

    I think unlinks could possibly cause problems and that's why I suggested we
    add sync() to the parent process before it runs the next iteration...

    > Did you receive my last couple of private emails commenting on the trace
    > data?
    Yes, I did get them. I'll reply to them in a while.

    Honza
    --
    Jan Kara <jack@suse.cz>
    SUSE Labs, CR


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