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    SubjectRe: [RFC PATCH 0/4] softirq: Per vector threading v3
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    On Tue, 2018-01-23 at 09:42 -0800, Linus Torvalds wrote:
    > On Tue, Jan 23, 2018 at 8:57 AM, Paolo Abeni <pabeni@redhat.com> wrote:
    > >
    > >> Or is it that the workqueue execution is simply not yielding for some
    > >> reason?
    > >
    > > It's like that.
    > >
    > > I spent little time on it, so I haven't many data point. I'll try to
    > > investigate the scenario later this week.
    >
    > Hmm. workqueues seem to use cond_resched_rcu_qs(), which does a
    > cond_resched() (and a RCU quiescent note).
    >
    > But I wonder if the test triggers the "lets run lots of workqueue
    > threads", and then the single-threaded user space just gets blown out
    > of the water by many kernel threads. Each thread gets its own "fair"
    > amount of CPU, but..

    If folks aren't careful with workqueues, they can be a generic
    starvation problem. Like the below in the here and now.

    fs/nfs: Add a resched point to nfs_commit_release_pages()

    During heavy NFS write, kworkers can do very large amounts of work
    without scheduling (82ms traced). Add a resched point.

    Signed-off-by: Mike Galbraith <efault@gmx.de>
    Suggested-by: Trond Myklebust <trondmy@primarydata.com>
    ---
    fs/nfs/write.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/fs/nfs/write.c
    +++ b/fs/nfs/write.c
    @@ -1837,6 +1837,7 @@ static void nfs_commit_release_pages(str
    set_bit(NFS_CONTEXT_RESEND_WRITES, &req->wb_context->flags);
    next:
    nfs_unlock_and_release_request(req);
    + cond_resched();
    }
    nfss = NFS_SERVER(data->inode);
    if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
    \
     
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      Last update: 2018-01-23 19:02    [W:2.846 / U:0.076 seconds]
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