From: David Vrabel <david.vrabel@citrix•com>
To: Wei Liu <wei.liu2@citrix•com>
Cc: <netdev@vger•kernel.org>, <xen-devel@lists•xen.org>,
Ian Campbell <ian.campbell@citrix•com>,
Zoltan Kiss <zoltan.kiss@citrix•com>
Subject: Re: [Xen-devel] [PATCH net v2 2/3] xen-netback: don't stop dealloc kthread too early
Date: Mon, 11 Aug 2014 15:34:48 +0100 [thread overview]
Message-ID: <53E8D488.1020305@citrix.com> (raw)
In-Reply-To: <20140811143107.GH3249@zion.uk.xensource.com>
On 11/08/14 15:31, Wei Liu wrote:
> On Mon, Aug 11, 2014 at 02:58:13PM +0100, David Vrabel wrote:
>> On 11/08/14 14:48, Wei Liu wrote:
>>> On Mon, Aug 11, 2014 at 01:10:12PM +0100, David Vrabel wrote:
>>>> On 08/08/14 17:37, Wei Liu wrote:
>>> [...]
>>>>> if (tx_evtchn == rx_evtchn) {
>>>>> /* feature-split-event-channels == 0 */
>>>>> @@ -687,6 +700,9 @@ void xenvif_disconnect(struct xenvif *vif)
>>>>> queue->task = NULL;
>>>>> }
>>>>>
>>>>> + wait_event(queue->inflight_wq,
>>>>> + atomic_read(&queue->inflight_packets) == 0);
>>>>
>>>> Just make the dealloc task not stop unless it has deallocated all
>>>> outstanding requests. There's no need for another wait queue here.
>>>>
>>>
>>> Are you suggesting something like
>>>
>>> while (atomic_read(&queue->inflight_packets) !=0)
>>> schedule_timeout(SOME_TIMEOUT);
>>
>> No. That would be awful!
>>
>> Add the test to the kthread itself:
>>
>> int xenvif_dealloc_kthread(void *data)
>> {
>> struct xenvif_queue *queue = data;
>>
>> while (atomic_read(&queue->inflight_packets) > 0
>> || !kthread_should_stop()) {
>> [...]
>>
>> etc.
>>
>> Although, the main loop is a bit confused, so I suggest adding:
>>
>> static bool xenvif_dealloc_thread_should_stop(struct xenvif_queue *q)
>> {
>> /* Dealloc thread must remain running if there are any inflight
>> * packets so it can properly dealloc them when they complete.
>> */
>> return atomic_read(&queue->inflight_packets) == 0
>> && kthread_should_stop();
>> }
>>
>> And cleaning it up a bit (the while() could be a for(;;)).
>>
>
> Unfortunately this approach is bogus. If xenbus thread is not blocked it
> can free up various resources while dealloc thread is running -- queue
> can be gone under dealloc thread's feet.
kthread_stop() waits until the thread exits (like pthread_join()).
/**
* kthread_stop - stop a thread created by kthread_create().
* @k: thread created by kthread_create().
*
* Sets kthread_should_stop() for @k to return true, wakes it, and
* waits for it to exit.
David
next prev parent reply other threads:[~2014-08-11 14:34 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-08 16:37 [PATCH net v2 0/3] xen-netback: synchronisation between core driver and netback Wei Liu
2014-08-08 16:37 ` [PATCH net v2 1/3] xen-netback: move NAPI add/remove calls Wei Liu
2014-08-08 16:49 ` Sergei Shtylyov
2014-08-08 16:52 ` Wei Liu
2014-08-11 12:35 ` [Xen-devel] " David Vrabel
2014-08-11 12:49 ` Zoltan Kiss
2014-08-11 13:01 ` David Vrabel
2014-08-11 13:14 ` Zoltan Kiss
2014-08-11 13:43 ` Wei Liu
2014-08-11 13:59 ` David Vrabel
2014-08-11 14:08 ` Wei Liu
2014-08-08 16:37 ` [PATCH net v2 2/3] xen-netback: don't stop dealloc kthread too early Wei Liu
2014-08-11 12:10 ` [Xen-devel] " David Vrabel
2014-08-11 13:48 ` Wei Liu
2014-08-11 13:58 ` David Vrabel
2014-08-11 14:13 ` Zoltan Kiss
2014-08-11 14:44 ` Wei Liu
2014-08-11 15:23 ` David Vrabel
2014-08-11 20:39 ` Wei Liu
2014-08-11 14:31 ` Wei Liu
2014-08-11 14:34 ` David Vrabel [this message]
2014-08-11 14:39 ` Wei Liu
2014-08-08 16:37 ` [PATCH net v2 3/3] xen-netback: remove loop waiting function Wei Liu
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