From: Paul Durrant <Paul.Durrant@citrix.com>
To: Anthony Perard <anthony.perard@citrix.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Anthony Perard <anthony.perard@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/2] xen-bus: Avoid rewriting identical values to xenstore
Date: Wed, 21 Aug 2019 15:40:05 +0000 [thread overview]
Message-ID: <703d5a46d4c74eb4afd93d76b7341efc@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <20190821092020.17952-3-anthony.perard@citrix.com>
> -----Original Message-----
> From: Anthony PERARD <anthony.perard@citrix.com>
> Sent: 21 August 2019 10:20
> To: qemu-devel@nongnu.org
> Cc: Anthony Perard <anthony.perard@citrix.com>; Stefano Stabellini <sstabellini@kernel.org>; Paul
> Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org
> Subject: [PATCH 2/2] xen-bus: Avoid rewriting identical values to xenstore
>
> When QEMU receive a xenstore watch event suggesting that the "state" or
> "online" status of the frontend or the backend changed, it record this
> in its own state but it also re-write the value back into xenstore even
> so there were no changed. This trigger an unnecessary xenstore watch
> event which QEMU will process again (and maybe the frontend as well).
>
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
> hw/xen/xen-bus.c | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> index 982eca4533..c83f07424a 100644
> --- a/hw/xen/xen-bus.c
> +++ b/hw/xen/xen-bus.c
> @@ -481,20 +481,27 @@ static int xen_device_backend_scanf(XenDevice *xendev, const char *key,
> return rc;
> }
>
> -void xen_device_backend_set_state(XenDevice *xendev,
> - enum xenbus_state state)
> +static bool xen_device_backend_record_state(XenDevice *xendev,
> + enum xenbus_state state)
> {
> const char *type = object_get_typename(OBJECT(xendev));
>
> if (xendev->backend_state == state) {
> - return;
> + return false;
> }
>
> trace_xen_device_backend_state(type, xendev->name,
> xs_strstate(state));
>
> xendev->backend_state = state;
> - xen_device_backend_printf(xendev, "state", "%u", state);
> + return true;
> +}
> +
> +void xen_device_backend_set_state(XenDevice *xendev,
> + enum xenbus_state state)
> +{
> + if (xen_device_backend_record_state(xendev, state))
> + xen_device_backend_printf(xendev, "state", "%u", state);
> }
>
> enum xenbus_state xen_device_backend_get_state(XenDevice *xendev)
> @@ -502,7 +509,8 @@ enum xenbus_state xen_device_backend_get_state(XenDevice *xendev)
> return xendev->backend_state;
> }
>
> -static void xen_device_backend_set_online(XenDevice *xendev, bool online)
> +static void xen_device_backend_set_online(XenDevice *xendev, bool online,
> + bool export)
> {
> const char *type = object_get_typename(OBJECT(xendev));
>
> @@ -513,7 +521,8 @@ static void xen_device_backend_set_online(XenDevice *xendev, bool online)
> trace_xen_device_backend_online(type, xendev->name, online);
>
> xendev->backend_online = online;
> - xen_device_backend_printf(xendev, "online", "%u", online);
> + if (export)
> + xen_device_backend_printf(xendev, "online", "%u", online);
> }
>
Perhaps the behaviour of backend_set_state() and backend_set_online() could be the same? I.e. they both take an 'export' (or perhaps 'publish'?) parameter and only write xenstore if that is true. (I realise that would involve modifying xen-block to pass 'true' as the extra export/publish param, but I think it would be neater overall).
> static void xen_device_backend_changed(void *opaque)
> @@ -529,13 +538,13 @@ static void xen_device_backend_changed(void *opaque)
> state = XenbusStateUnknown;
> }
>
> - xen_device_backend_set_state(xendev, state);
> + xen_device_backend_record_state(xendev, state);
>
> if (xen_device_backend_scanf(xendev, "online", "%u", &online) != 1) {
> online = 0;
> }
>
> - xen_device_backend_set_online(xendev, !!online);
> + xen_device_backend_set_online(xendev, !!online, false);
>
You could then pass 'false' here in both cases.
> /*
> * If the toolstack (or unplug request callback) has set the backend
> @@ -683,7 +692,8 @@ int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
> }
>
> static void xen_device_frontend_set_state(XenDevice *xendev,
> - enum xenbus_state state)
> + enum xenbus_state state,
> + bool export)
> {
> const char *type = object_get_typename(OBJECT(xendev));
>
> @@ -695,7 +705,8 @@ static void xen_device_frontend_set_state(XenDevice *xendev,
> xs_strstate(state));
>
> xendev->frontend_state = state;
> - xen_device_frontend_printf(xendev, "state", "%u", state);
> + if (export)
> + xen_device_frontend_printf(xendev, "state", "%u", state);
> }
>
> static void xen_device_frontend_changed(void *opaque)
> @@ -711,7 +722,7 @@ static void xen_device_frontend_changed(void *opaque)
> state = XenbusStateUnknown;
> }
>
> - xen_device_frontend_set_state(xendev, state);
> + xen_device_frontend_set_state(xendev, state, false);
>
> if (state == XenbusStateInitialising &&
> xendev->backend_state == XenbusStateClosed &&
> @@ -1146,7 +1157,7 @@ static void xen_device_realize(DeviceState *dev, Error **errp)
> xendev->frontend_id);
> xen_device_backend_printf(xendev, "hotplug-status", "connected");
>
> - xen_device_backend_set_online(xendev, true);
> + xen_device_backend_set_online(xendev, true, true);
> xen_device_backend_set_state(xendev, XenbusStateInitWait);
>
> xen_device_frontend_printf(xendev, "backend", "%s",
> @@ -1154,7 +1165,7 @@ static void xen_device_realize(DeviceState *dev, Error **errp)
> xen_device_frontend_printf(xendev, "backend-id", "%u",
> xenbus->backend_id);
>
> - xen_device_frontend_set_state(xendev, XenbusStateInitialising);
> + xen_device_frontend_set_state(xendev, XenbusStateInitialising, true);
>
And similarly pass 'true' here for all three cases.
What do you think?
Paul
> xendev->exit.notify = xen_device_exit;
> qemu_add_exit_notifier(&xendev->exit);
> --
> Anthony PERARD
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Xen-devel mailing list
Xen-devel@lists.xenproject.org
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next prev parent reply other threads:[~2019-08-21 15:40 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190821092020.17952-1-anthony.perard@citrix.com>
2019-08-21 9:20 ` [Xen-devel] [PATCH 1/2] xen-bus: Fix backend state transition on device reset Anthony PERARD
2019-08-21 9:36 ` Paul Durrant
2019-08-22 9:50 ` Anthony PERARD
2019-08-22 9:59 ` Paul Durrant
2019-08-22 15:01 ` Anthony PERARD
2019-08-21 9:20 ` [Xen-devel] [PATCH 2/2] xen-bus: Avoid rewriting identical values to xenstore Anthony PERARD
2019-08-21 15:40 ` Paul Durrant [this message]
2019-08-22 10:21 ` Anthony PERARD
2019-08-22 10:36 ` Paul Durrant
2019-08-22 11:17 ` Anthony PERARD
2019-08-22 11:25 ` Paul Durrant
2019-08-22 13:18 ` Anthony PERARD
2019-08-22 13:21 ` Paul Durrant
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