Re: [Xen-devel] [PATCH 16/19] libxl: suspend: Abolish usleeps in domain suspend wait

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-03-04 at 14:56 +0000, Ian Jackson wrote:
> Replace the use of a loop with usleep().
> 
> Instead, use a xenstore watch and an event system timeout.  xenstore
> fires watches on @releaseDomain when a domain shuts down.
> 
> The logic which checks for the state of the domain is unchanged, and
> not ideal, but we will leave that for the next patch.
> 
> There is not intended to be any semantic change, other than to make
> the algorithm properly asynchronous and the consequential waiting on
> xenstore, rather than polling.
> 
> Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
>  tools/libxl/libxl_dom.c      |   80 
> ++++++++++++++++++++++++++++++------------
>  tools/libxl/libxl_internal.h |    2 ++
>  2 files changed, 60 insertions(+), 22 deletions(-)
> 
> diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
> index dde7e33..6291115 100644
> --- a/tools/libxl/libxl_dom.c
> +++ b/tools/libxl/libxl_dom.c
> @@ -1028,8 +1028,14 @@ static void 
> domain_suspend_common_wait_guest(libxl__egc *egc,
>                                               libxl__domain_suspend_state 
> *dss);
>  static void domain_suspend_common_guest_suspended(libxl__egc *egc,
>                                           libxl__domain_suspend_state *dss);
> +
>  static void domain_suspend_common_pvcontrol_suspending(libxl__egc *egc,
>        libxl__xswait_state *xswa, int rc, const char *state);
> +static void suspend_common_wait_guest_watch(libxl__egc *egc,
> +      libxl__ev_xswatch *xsw, const char *watch_path, const char 
> *event_path);
> +static void suspend_common_wait_guest_timeout(libxl__egc *egc,
> +      libxl__ev_time *ev, const struct timeval *requested_abs);
> +
>  static void domain_suspend_common_failed(libxl__egc *egc,
>                                           libxl__domain_suspend_state *dss);
>  static void domain_suspend_common_done(libxl__egc *egc,
> @@ -1175,36 +1181,59 @@ static void 
> domain_suspend_common_wait_guest(libxl__egc *egc,
>                                               libxl__domain_suspend_state 
> *dss)
>  {
>      STATE_AO_GC(dss->ao);
> +    int rc;
> +
> +    LOG(DEBUG, "wait for the guest to suspend");
> +
> +    rc = libxl__ev_xswatch_register(gc, &dss->guest_watch,
> +                                    suspend_common_wait_guest_watch,
> +                                    "@releaseDomain");
> +    if (rc) goto err;
> +
> +    rc = libxl__ev_time_register_rel(gc, &dss->guest_timeout, 
> +                                     suspend_common_wait_guest_timeout,
> +                                     60*1000);

This smells a lot like the xswait stuff you introduced towards the
beginning of the series.

Is the difference just that you cannot read the "path" @releaseDomain?
If so can we paper over that somehow in the helper?

Ian.


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