| Message ID | 4DFAAF00.900@cn.fujitsu.com |
|---|---|
| State | New |
| Headers | show |
Am 17.06.2011 03:33, schrieb Wen Congyang: > If !s->clock_enabled or !rtl8139_receiver_enabled(s), it means that > the nic will drop all packets from host. So qemu will keep getting > packets from host and wasting CPU on dropping packets. This seems > worse than packets that should be dropped but aren't. > > Signed-off-by: Wen Congyang <wency@cn.fujitsu.com> Which bug does this change fix? I'm still not convinced that we should do it. > --- > hw/rtl8139.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/hw/rtl8139.c b/hw/rtl8139.c > index 2f8db58..9084678 100644 > --- a/hw/rtl8139.c > +++ b/hw/rtl8139.c > @@ -810,9 +810,9 @@ static int rtl8139_can_receive(VLANClientState *nc) > > /* Receive (drop) packets if card is disabled. */ This comment isn't accurate any more after applying the patch. > if (!s->clock_enabled) > - return 1; > + return 0; > if (!rtl8139_receiver_enabled(s)) > - return 1; > + return 0; > > if (rtl8139_cp_receiver_enabled(s)) { > /* ??? Flow control not implemented in c+ mode. > -- 1.7.1 Kevin
At 06/20/2011 05:10 PM, Kevin Wolf Write: > Am 17.06.2011 03:33, schrieb Wen Congyang: >> If !s->clock_enabled or !rtl8139_receiver_enabled(s), it means that >> the nic will drop all packets from host. So qemu will keep getting >> packets from host and wasting CPU on dropping packets. This seems >> worse than packets that should be dropped but aren't. >> >> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com> > > Which bug does this change fix? I'm still not convinced that we should > do it. Maybe not a bug fix now. As Michael S. Tsirkin said, if rtl8139_can_receive() returns 1, qemu will keep getting packets from host and wasting CPU on dropping packets. We can save CPU by return 0. > >> --- >> hw/rtl8139.c | 4 ++-- >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/hw/rtl8139.c b/hw/rtl8139.c >> index 2f8db58..9084678 100644 >> --- a/hw/rtl8139.c >> +++ b/hw/rtl8139.c >> @@ -810,9 +810,9 @@ static int rtl8139_can_receive(VLANClientState *nc) >> >> /* Receive (drop) packets if card is disabled. */ > > This comment isn't accurate any more after applying the patch. > >> if (!s->clock_enabled) >> - return 1; >> + return 0; >> if (!rtl8139_receiver_enabled(s)) >> - return 1; >> + return 0; >> >> if (rtl8139_cp_receiver_enabled(s)) { >> /* ??? Flow control not implemented in c+ mode. >> -- 1.7.1 > > Kevin >
Am 20.06.2011 11:40, schrieb Wen Congyang: > At 06/20/2011 05:10 PM, Kevin Wolf Write: >> Am 17.06.2011 03:33, schrieb Wen Congyang: >>> If !s->clock_enabled or !rtl8139_receiver_enabled(s), it means that >>> the nic will drop all packets from host. So qemu will keep getting >>> packets from host and wasting CPU on dropping packets. This seems >>> worse than packets that should be dropped but aren't. >>> >>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com> >> >> Which bug does this change fix? I'm still not convinced that we should >> do it. > > Maybe not a bug fix now. As Michael S. Tsirkin said, if rtl8139_can_receive() > returns 1, qemu will keep getting packets from host and wasting CPU on > dropping packets. We can save CPU by return 0. Don't we waste memory instead then because we leave the packets queued indefinitely? Kevin
On Mon, Jun 20, 2011 at 11:52:20AM +0200, Kevin Wolf wrote: > Am 20.06.2011 11:40, schrieb Wen Congyang: > > At 06/20/2011 05:10 PM, Kevin Wolf Write: > >> Am 17.06.2011 03:33, schrieb Wen Congyang: > >>> If !s->clock_enabled or !rtl8139_receiver_enabled(s), it means that > >>> the nic will drop all packets from host. So qemu will keep getting > >>> packets from host and wasting CPU on dropping packets. This seems > >>> worse than packets that should be dropped but aren't. > >>> > >>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com> > >> > >> Which bug does this change fix? I'm still not convinced that we should > >> do it. > > > > Maybe not a bug fix now. As Michael S. Tsirkin said, if rtl8139_can_receive() > > returns 1, qemu will keep getting packets from host and wasting CPU on > > dropping packets. We can save CPU by return 0. > > Don't we waste memory instead then because we leave the packets queued > indefinitely? > > Kevin Yes but the amount of wasted memory is bound from above so this doesn't seem too bad to me ...
diff --git a/hw/rtl8139.c b/hw/rtl8139.c index 2f8db58..9084678 100644 --- a/hw/rtl8139.c +++ b/hw/rtl8139.c @@ -810,9 +810,9 @@ static int rtl8139_can_receive(VLANClientState *nc) /* Receive (drop) packets if card is disabled. */ if (!s->clock_enabled) - return 1; + return 0; if (!rtl8139_receiver_enabled(s)) - return 1; + return 0; if (rtl8139_cp_receiver_enabled(s)) { /* ??? Flow control not implemented in c+ mode.
If !s->clock_enabled or !rtl8139_receiver_enabled(s), it means that the nic will drop all packets from host. So qemu will keep getting packets from host and wasting CPU on dropping packets. This seems worse than packets that should be dropped but aren't. Signed-off-by: Wen Congyang <wency@cn.fujitsu.com> --- hw/rtl8139.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) -- 1.7.1