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    SubjectRe: [patch] voluntary-preempt-

    * K.R. Foley <> wrote:

    > Here is a latency trace generated by the NFS compile in the
    > stress-kernel. It is ~1.7 ms which doesn't really surprise me for the
    > NFS compile. I am going to take the NFS compile out of the test now
    > and see what else falls out.

    NFS uses lock_kernel() for most of its locking. This means that the
    sharing and locking rules and assumptions are not clear (it's all within
    this opaque lock). I tried to figure out whether it would be safe to do
    a lock-break in nfs_cached_lookup() but it's quite hard ... Please bug
    the NFS-client maintainer(s) about this. To break this latency we'd have
    to do a lock-break in fs/nfs/dir.c:nfs_cached_lookup()'s main loop:

    for(;(page = find_get_page(dir->i_mapping, desc.page_index)); desc.page_index++) {

    res = -EIO;

    you could try this at the end of the loop:

    if (res == 0)
    goto out_found;
    if (res != -EAGAIN)
    + cond_resched();

    but i cannot guarantee that this is correct ... It might seem to work
    now but break later under load, etc. It's the NFS maintainer's call.

    > If it would be useful for me to provide additional information with
    > this, please let me know.

    reports like this are perfect for most latencies. I tried to include
    everything that is needed normally in /proc/latency_trace itself.

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      Last update: 2005-03-22 14:05    [W:0.022 / U:0.752 seconds]
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