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Groups > linux.kernel > #1448512
| From | Bob Liu <bob.liu@oracle.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources |
| Date | 2016-07-22 11:50 +0200 |
| Message-ID | <rXFfI-429-11@gated-at.bofh.it> (permalink) |
| References | (2 earlier) <rXhZL-57r-7@gated-at.bofh.it> <rXj5v-63Y-7@gated-at.bofh.it> <rXDnz-2NF-9@gated-at.bofh.it> <rXDQC-3e4-7@gated-at.bofh.it> <rXF62-3XU-17@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 07/22/2016 05:34 PM, Roger Pau Monné wrote:
> On Fri, Jul 22, 2016 at 04:17:48PM +0800, Bob Liu wrote:
>>
>> On 07/22/2016 03:45 PM, Roger Pau Monné wrote:
>>> On Thu, Jul 21, 2016 at 06:08:05PM +0800, Bob Liu wrote:
>>>>
>>>> On 07/21/2016 04:57 PM, Roger Pau Monné wrote:
>> ..[snip]..
>>>>>> +
>>>>>> +static ssize_t dynamic_reconfig_device(struct blkfront_info *info, ssize_t count)
>>>>>> +{
>>>>>> + unsigned int i;
>>>>>> + int err = -EBUSY;
>>>>>> +
>>>>>> + /*
>>>>>> + * Make sure no migration in parallel, device lock is actually a
>>>>>> + * mutex.
>>>>>> + */
>>>>>> + if (!device_trylock(&info->xbdev->dev)) {
>>>>>> + pr_err("Fail to acquire dev:%s lock, may be in migration.\n",
>>>>>> + dev_name(&info->xbdev->dev));
>>>>>> + return err;
>>>>>> + }
>>>>>> +
>>>>>> + /*
>>>>>> + * Prevent new requests and guarantee no uncompleted reqs.
>>>>>> + */
>>>>>> + blk_mq_freeze_queue(info->rq);
>>>>>> + if (part_in_flight(&info->gd->part0))
>>>>>> + goto out;
>>>>>> +
>>>>>> + /*
>>>>>> + * Front Backend
>>>>>> + * Switch to XenbusStateClosed
>>>>>> + * frontend_changed():
>>>>>> + * case XenbusStateClosed:
>>>>>> + * xen_blkif_disconnect()
>>>>>> + * Switch to XenbusStateClosed
>>>>>> + * blkfront_resume():
>>>>>> + * frontend_changed():
>>>>>> + * reconnect
>>>>>> + * Wait until XenbusStateConnected
>>>>>> + */
>>>>>> + info->reconfiguring = true;
>>>>>> + xenbus_switch_state(info->xbdev, XenbusStateClosed);
>>>>>> +
>>>>>> + /* Poll every 100ms, 1 minute timeout. */
>>>>>> + for (i = 0; i < 600; i++) {
>>>>>> + /*
>>>>>> + * Wait backend enter XenbusStateClosed, blkback_changed()
>>>>>> + * will clear reconfiguring.
>>>>>> + */
>>>>>> + if (!info->reconfiguring)
>>>>>> + goto resume;
>>>>>> + schedule_timeout_interruptible(msecs_to_jiffies(100));
>>>>>> + }
>>>>>
>>>>> Instead of having this wait, could you just set info->reconfiguring = 1, set
>>>>> the frontend state to XenbusStateClosed and mimic exactly what a resume from
>>>>> suspension does? blkback_changed would have to set the frontend state to
>>>>> InitWait when it detects that the backend has switched to Closed, and call
>>>>> blkfront_resume.
>>>>
>>>>
>>>> I think that won't work.
>>>> In the real "resume" case, the power management system will trigger all ->resume() path.
>>>> But there is no place for dynamic configuration.
>>>
>>> Hello,
>>>
>>> I think it should be possible to set info->reconfiguring and wait for the
>>> backend to switch to state Closed, at that point we should call blkif_resume
>>> (from blkback_changed) and the backend will follow the reconection.
>>>
>>
>> Okay, I get your point. Yes, that's an option.
>>
>> But this will make 'dynamic configuration' to be async, I'm worry about the end-user will get panic.
>> E.g
>> A end-user "echo <new value> > /sys/devices/vbd-xxx/max_indirect_segs",
>> but then the device will be Closed and disappeared, the user have to wait for a random time so that the device can resume.
>
> That should not happen, AFAICT on migration the device never dissapears.
Oh, yes.
> alloc_disk and friends should not be called on resume from migration (see
> the switch in blkfront_connect, you should take the BLKIF_STATE_SUSPENDED
> path for the reconfiguration).
>
What about if the end-user starts I/O immediately after writing new value to /sys?
But the resume is still in progress.
--
Regards,
-Bob
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[PATCH 1/3] xen-blkfront: fix places not updated after introducing 64KB page granularity Bob Liu <bob.liu@oracle.com> - 2016-07-15 11:40 +0200
[PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-15 11:40 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-21 11:00 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-21 12:10 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-22 09:50 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-22 10:20 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-22 11:40 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-22 11:50 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-22 13:50 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-23 00:20 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-25 11:30 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-25 12:30 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-25 13:00 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-25 13:10 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Roger Pau Monné <roger.pau@citrix.com> - 2016-07-25 14:20 +0200
Re: [PATCH 3/3] xen-blkfront: dynamic configuration of per-vbd resources Bob Liu <bob.liu@oracle.com> - 2016-07-25 14:30 +0200
[PATCH 2/3] xen-blkfront: introduce blkif_set_queue_limits() Bob Liu <bob.liu@oracle.com> - 2016-07-15 11:40 +0200
Re: [PATCH 2/3] xen-blkfront: introduce blkif_set_queue_limits() Roger Pau Monné <roger.pau@citrix.com> - 2016-07-21 10:30 +0200
Re: [PATCH 2/3] xen-blkfront: introduce blkif_set_queue_limits() Bob Liu <bob.liu@oracle.com> - 2016-07-21 11:50 +0200
Re: [PATCH 1/3] xen-blkfront: fix places not updated after introducing 64KB page granularity Roger Pau Monné <roger.pau@citrix.com> - 2016-07-21 10:10 +0200
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