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    SubjectRe: [-next regression] TCP window full with EPOLLWAKEUP
    Date
    On Sunday, May 20, 2012, Rafael J. Wysocki wrote:
    > On Sunday, May 20, 2012, Jiri Slaby wrote:
    > > Hi,
    > >
    > > a bisection shows that with the following commit from -next:
    > > commit 4d7e30d98939a0340022ccd49325a3d70f7e0238
    > > Author: Arve Hjønnevåg <arve@android.com>
    > > Date: Tue May 1 21:33:34 2012 +0200
    > >
    > > epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll
    > > events are ready
    > >
    > > ====
    > >
    > > one of mono programs I use stops receiving data from the network.
    > > Wireshark shows that the TCP window of a connection is filled. This
    > > means the program does not read the data fast enough after requesting
    > > the data.
    > >
    > > If I revert that commit on the top of -next (20120518), everything works
    > > as expected.
    >
    > Hmm. I suppose that the failing program doesn't set EPOLLWAKEUP by mistake,
    > does it?

    If it doesn't, we can assume that epi-ws is always NULL and all of the added
    overhead comes from the function calls. So, I wonder if the appended patch
    makes any difference?

    Rafael


    ---
    fs/eventpoll.c | 35 ++++++++++++++++++++++++-----------
    1 file changed, 24 insertions(+), 11 deletions(-)

    Index: linux/fs/eventpoll.c
    ===================================================================
    --- linux.orig/fs/eventpoll.c
    +++ linux/fs/eventpoll.c
    @@ -597,7 +597,8 @@ static int ep_scan_ready_list(struct eve
    */
    if (!ep_is_linked(&epi->rdllink)) {
    list_add_tail(&epi->rdllink, &ep->rdllist);
    - __pm_stay_awake(epi->ws);
    + if (epi->ws)
    + __pm_stay_awake(epi->ws);
    }
    }
    /*
    @@ -611,7 +612,8 @@ static int ep_scan_ready_list(struct eve
    * Quickly re-inject items left on "txlist".
    */
    list_splice(&txlist, &ep->rdllist);
    - __pm_relax(ep->ws);
    + if (ep->ws)
    + __pm_relax(ep->ws);

    if (!list_empty(&ep->rdllist)) {
    /*
    @@ -750,7 +752,9 @@ static int ep_read_events_proc(struct ev
    * callback, but it's not actually ready, as far as
    * caller requested events goes. We can remove it here.
    */
    - __pm_relax(epi->ws);
    + if (epi->ws)
    + __pm_relax(epi->ws);
    +
    list_del_init(&epi->rdllink);
    }
    }
    @@ -956,7 +960,8 @@ static int ep_poll_callback(wait_queue_t
    /* If this file is already in the ready list we exit soon */
    if (!ep_is_linked(&epi->rdllink)) {
    list_add_tail(&epi->rdllink, &ep->rdllist);
    - __pm_stay_awake(epi->ws);
    + if (epi->ws)
    + __pm_stay_awake(epi->ws);
    }

    /*
    @@ -1219,7 +1224,8 @@ static int ep_insert(struct eventpoll *e
    /* If the file is already "ready" we drop it inside the ready list */
    if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
    list_add_tail(&epi->rdllink, &ep->rdllist);
    - __pm_stay_awake(epi->ws);
    + if (epi->ws)
    + __pm_stay_awake(epi->ws);

    /* Notify waiting tasks that events are available */
    if (waitqueue_active(&ep->wq))
    @@ -1309,7 +1315,8 @@ static int ep_modify(struct eventpoll *e
    spin_lock_irq(&ep->lock);
    if (!ep_is_linked(&epi->rdllink)) {
    list_add_tail(&epi->rdllink, &ep->rdllist);
    - __pm_stay_awake(epi->ws);
    + if (epi->ws)
    + __pm_stay_awake(epi->ws);

    /* Notify waiting tasks that events are available */
    if (waitqueue_active(&ep->wq))
    @@ -1357,9 +1364,12 @@ static int ep_send_events_proc(struct ev
    * instead, but then epi->ws would temporarily be out of sync
    * with ep_is_linked().
    */
    - if (epi->ws && epi->ws->active)
    - __pm_stay_awake(ep->ws);
    - __pm_relax(epi->ws);
    + if (epi->ws) {
    + if (epi->ws->active)
    + __pm_stay_awake(ep->ws);
    +
    + __pm_relax(epi->ws);
    + }
    list_del_init(&epi->rdllink);

    pt._key = epi->event.events;
    @@ -1376,7 +1386,9 @@ static int ep_send_events_proc(struct ev
    if (__put_user(revents, &uevent->events) ||
    __put_user(epi->event.data, &uevent->data)) {
    list_add(&epi->rdllink, head);
    - __pm_stay_awake(epi->ws);
    + if (epi->ws)
    + __pm_stay_awake(epi->ws);
    +
    return eventcnt ? eventcnt : -EFAULT;
    }
    eventcnt++;
    @@ -1396,7 +1408,8 @@ static int ep_send_events_proc(struct ev
    * poll callback will queue them in ep->ovflist.
    */
    list_add_tail(&epi->rdllink, &ep->rdllist);
    - __pm_stay_awake(epi->ws);
    + if (epi->ws)
    + __pm_stay_awake(epi->ws);
    }
    }
    }
    --
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