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d="scan'208";a="4748662" From: Paul Durrant To: Anthony Perard , "qemu-devel@nongnu.org" Thread-Topic: [PATCH v2 2/2] xen-bus: Avoid rewriting identical values to xenstore Thread-Index: AQHVWZu4AfJbcgj9V0CJghQKigFNTacOxSww Date: Tue, 27 Aug 2019 09:46:15 +0000 Message-ID: <322ae907c2594237bdc7b63a24f63bab@AMSPEX02CL03.citrite.net> References: <20190823101534.465-1-anthony.perard@citrix.com> <20190823101534.465-3-anthony.perard@citrix.com> In-Reply-To: <20190823101534.465-3-anthony.perard@citrix.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: FreeBSD 9.x X-Received-From: 216.71.145.153 Subject: Re: [Qemu-devel] [PATCH v2 2/2] xen-bus: Avoid rewriting identical values to xenstore X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Anthony Perard , "xen-devel@lists.xenproject.org" , Stefano Stabellini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > -----Original Message----- > From: Anthony PERARD > Sent: 23 August 2019 11:16 > To: qemu-devel@nongnu.org > Cc: Anthony Perard ; Stefano Stabellini ; Paul > Durrant ; xen-devel@lists.xenproject.org > Subject: [PATCH v2 2/2] xen-bus: Avoid rewriting identical values to xens= tore >=20 > When QEMU receives a xenstore watch event suggesting that the "state" > of the frontend changed, it records this in its own state but it also > re-write the value back into xenstore even so there were no change. > This triggers an unnecessary xenstore watch event which QEMU will > process again (and maybe the frontend as well). Also QEMU could > potentially write an already old value. >=20 > Signed-off-by: Anthony PERARD Reviewed-by: Paul Durrant > --- >=20 > Notes: > v2: > - fix coding style > - only change frontend_set_state() and use 'publish' instead of 'expo= rt'. >=20 > hw/xen/xen-bus.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) >=20 > diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c > index 62c127b926..a04478ad4f 100644 > --- a/hw/xen/xen-bus.c > +++ b/hw/xen/xen-bus.c > @@ -698,7 +698,8 @@ int xen_device_frontend_scanf(XenDevice *xendev, cons= t char *key, > } >=20 > static void xen_device_frontend_set_state(XenDevice *xendev, > - enum xenbus_state state) > + enum xenbus_state state, > + bool publish) > { > const char *type =3D object_get_typename(OBJECT(xendev)); >=20 > @@ -710,7 +711,9 @@ static void xen_device_frontend_set_state(XenDevice *= xendev, > xs_strstate(state)); >=20 > xendev->frontend_state =3D state; > - xen_device_frontend_printf(xendev, "state", "%u", state); > + if (publish) { > + xen_device_frontend_printf(xendev, "state", "%u", state); > + } > } >=20 > static void xen_device_frontend_changed(void *opaque) > @@ -726,7 +729,7 @@ static void xen_device_frontend_changed(void *opaque) > state =3D XenbusStateUnknown; > } >=20 > - xen_device_frontend_set_state(xendev, state); > + xen_device_frontend_set_state(xendev, state, false); >=20 > if (state =3D=3D XenbusStateInitialising && > xendev->backend_state =3D=3D XenbusStateClosed && > @@ -1169,7 +1172,7 @@ static void xen_device_realize(DeviceState *dev, Er= ror **errp) > xen_device_frontend_printf(xendev, "backend-id", "%u", > xenbus->backend_id); >=20 > - xen_device_frontend_set_state(xendev, XenbusStateInitialising); > + xen_device_frontend_set_state(xendev, XenbusStateInitialising, true)= ; >=20 > xendev->exit.notify =3D xen_device_exit; > qemu_add_exit_notifier(&xendev->exit); > -- > Anthony PERARD