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SubjectRE: Introduce xenwatch multithreading (mtwatch)
Date
> -----Original Message-----
> From: Dongli Zhang [mailto:dongli.zhang@oracle.com]
> Sent: 14 September 2018 08:34
> To: xen-devel@lists.xenproject.org; linux-kernel@vger.kernel.org
> Cc: boris.ostrovsky@oracle.com; jgross@suse.com; Paul Durrant
> <Paul.Durrant@citrix.com>; Wei Liu <wei.liu2@citrix.com>;
> konrad.wilk@oracle.com; Roger Pau Monne <roger.pau@citrix.com>;
> srinivas.eeda@oracle.com
> Subject: Introduce xenwatch multithreading (mtwatch)
>
> Hi,
>
> This patch set introduces xenwatch multithreading (mtwatch) based on the
> below xen summit 2018 design session notes:

Ah, here is the cover letter... just not labelled 0/6.

>
> https://lists.xenproject.org/archives/html/xen-devel/2018-07/msg00017.html
>
>
> xenwatch_thread is a single kernel thread processing the callback function
> for subscribed xenwatch events successively. The xenwatch is stalled in
> 'D'
> state if any of callback function is stalled and uninterruptible.
>
> The domU

I think you should use 'frontend'. It is perfectly possible that a frontend could run in dom0m if, say, the system were using a driver domain.

> create/destroy is failed if xenwatch is stalled in 'D' state as
> the paravirtual driver init/uninit cannot complete. Usually, the only
> option is to reboot dom0 server unless there is solution/workaround to

Similarly 'backend' instead of 'dom0', pointing out that this is bad because it is normal for a single backend domain to serve multiple frontend domains, and the PV protocol is not (yet) re-startable if a backend goes away.

Paul

> move forward and complete the stalled xenwatch event callback function.
> Below is the output of 'xl create' when xenwatch is stalled (the issue is
> reproduced on purpose by hooking netif_receive_skb() to intercept an
> sk_buff sent out from vifX.Y on dom0 with patch at
> https://github.com/finallyjustice/patchset/blob/master/xenwatch-stall-by-
> vif.patch):
>
> # xl create pv.cfg
> Parsing config from pv.cfg
> libxl: error: libxl_device.c:1080:device_backend_callback: Domain 2:unable
> to add device with path /local/domain/0/backend/vbd/2/51712
> libxl: error: libxl_create.c:1278:domcreate_launch_dm: Domain 2:unable to
> add disk devices
> libxl: error: libxl_device.c:1080:device_backend_callback: Domain 2:unable
> to remove device with path /local/domain/0/backend/vbd/2/51712
> libxl: error: libxl_domain.c:1073:devices_destroy_cb: Domain
> 2:libxl__devices_destroy failed
> libxl: error: libxl_domain.c:1000:libxl__destroy_domid: Domain 2:Non-
> existant domain
> libxl: error: libxl_domain.c:959:domain_destroy_callback: Domain 2:Unable
> to destroy guest
> libxl: error: libxl_domain.c:886:domain_destroy_cb: Domain 2:Destruction
> of domain failed
>
>
> The idea of this patch set is to create a per-domU xenwatch thread for
> each
> domid. The per-domid thread is created when the 1st pv backend device (for
> this domid and with xenwatch multithreading enabled) is created, while
> this
> thread is destroyed when the last pv backend device (for this domid and
> with xenwatch multithreading enabled) is removed. Per-domid xs_watch_event
> is never put on the default event list, but is put on the per-domid event
> list directly.
>
>
> For more details, please refer to the xen summit 2018 design session notes
> and presentation slides:
>
> https://lists.xenproject.org/archives/html/xen-devel/2018-07/msg00017.html
> http://www.donglizhang.org/xenwatch_multithreading.pdf
>
> ----------------------------------------------------------------
>
> Dongli Zhang (6):
> xenbus: prepare data structures and parameter for xenwatch
> multithreading
> xenbus: implement the xenwatch multithreading framework
> xenbus: dispatch per-domU watch event to per-domU xenwatch thread
> xenbus: process otherend_watch event at 'state' entry in xenwatch
> multithreading
> xenbus: process be_watch events in xenwatch multithreading
> drivers: enable xenwatch multithreading for xen-netback and xen-
> blkback driver
>
> Documentation/admin-guide/kernel-parameters.txt | 3 +
> drivers/block/xen-blkback/xenbus.c | 3 +-
> drivers/net/xen-netback/xenbus.c | 1 +
> drivers/xen/xenbus/xenbus_probe.c | 24 +-
> drivers/xen/xenbus/xenbus_probe_backend.c | 32 +++
> drivers/xen/xenbus/xenbus_xs.c | 357
> +++++++++++++++++++++++-
> include/xen/xenbus.h | 70 +++++
> 7 files changed, 484 insertions(+), 6 deletions(-)
>
> Thank you very much!
>
> Dongli Zhang

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