linux-kernel - Re: Introduce xenwatch multithreading (mtwatch)

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Date:   Fri, 14 Sep 2018 11:18:35 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     boris.ostrovsky@...cle.com, paul.durrant@...rix.com,
        wei.liu2@...rix.com, konrad.wilk@...cle.com, roger.pau@...rix.com,
        srinivas.eeda@...cle.com
Subject: Re: Introduce xenwatch multithreading (mtwatch)

On 14/09/18 09:34, Dongli Zhang wrote:
> Hi,
> 
> This patch set introduces xenwatch multithreading (mtwatch) based on the
> below xen summit 2018 design session notes:
> 
> 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 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
> 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!

One general remark regarding your commit messages: Please drop the
patch number from the text itself, its enough to have it in the mail
subject line. Later it is completely irrelevant in git history.


Juergen