lkml.org 
[lkml]   [2010]   [Jul]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH UPDATED 1/3] vhost: replace vhost_workqueue with per-vhost kthread
    On Thu, Jul 22, 2010 at 11:21:40PM +0200, Tejun Heo wrote:
    > Hello,
    >
    > On 07/22/2010 05:58 PM, Michael S. Tsirkin wrote:
    > > All the tricky barrier pairing made me uncomfortable. So I came up with
    > > this on top (untested): if we do all operations under the spinlock, we
    > > can get by without barriers and atomics. And since we need the lock for
    > > list operations anyway, this should have no paerformance impact.
    > >
    > > What do you think?
    >
    > I've created kthread_worker in wq#for-next tree and already converted
    > ivtv to use it. Once this lands in mainline, I think converting vhost
    > to use it would be better choice. kthread worker code uses basically
    > the same logic used in the vhost_workqueue code but is better
    > organized and documented. So, I think it would be better to stick
    > with the original implementation, as otherwise we're likely to just
    > decrease test coverage without much gain.
    >
    > http://git.kernel.org/?p=linux/kernel/git/tj/wq.git;a=commitdiff;h=b56c0d8937e665a27d90517ee7a746d0aa05af46;hp=53c5f5ba42c194cb13dd3083ed425f2c5b1ec439

    Sure, if we keep using workqueue. But I'd like to investigate this
    direction a bit more because there's discussion to switching from kthread to
    regular threads altogether.

    > > @@ -151,37 +161,37 @@ static void vhost_vq_reset(struct vhost_dev *dev,
    > > static int vhost_worker(void *data)
    > > {
    > > struct vhost_dev *dev = data;
    > > - struct vhost_work *work;
    > > + struct vhost_work *work = NULL;
    > >
    > > -repeat:
    > > - set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
    > > + for (;;) {
    > > + set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
    > >
    > > - if (kthread_should_stop()) {
    > > - __set_current_state(TASK_RUNNING);
    > > - return 0;
    > > - }
    > > + if (kthread_should_stop()) {
    > > + __set_current_state(TASK_RUNNING);
    > > + return 0;
    > > + }
    > >
    > > - work = NULL;
    > > - spin_lock_irq(&dev->work_lock);
    > > - if (!list_empty(&dev->work_list)) {
    > > - work = list_first_entry(&dev->work_list,
    > > - struct vhost_work, node);
    > > - list_del_init(&work->node);
    > > - }
    > > - spin_unlock_irq(&dev->work_lock);
    > > + spin_lock_irq(&dev->work_lock);
    > > + if (work) {
    > > + work->done_seq = work->queue_seq;
    > > + if (work->flushing)
    > > + wake_up_all(&work->done);
    >
    > I don't think doing this before executing the function is correct,

    Well, before I execute the function work is NULL, so this is skipped.
    Correct?

    > so
    > you'll have to release the lock, execute the function, regrab the lock
    > and then do the flush processing.
    >
    > Thanks.

    It's done in the loop, so I thought we can reuse the locking
    done for the sake of processing the next work item.
    Makes sense?


    > --
    > tejun


    \
     
     \ /
      Last update: 2010-07-24 21:23    [W:0.029 / U:0.812 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site