From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55849) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uft8Z-0008O8-A3 for qemu-devel@nongnu.org; Fri, 24 May 2013 10:38:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Uft8S-0005Hs-B5 for qemu-devel@nongnu.org; Fri, 24 May 2013 10:38:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44874) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uft8S-0005Ha-0Y for qemu-devel@nongnu.org; Fri, 24 May 2013 10:38:24 -0400 From: Stefan Hajnoczi Date: Fri, 24 May 2013 16:38:15 +0200 Message-Id: <1369406295-20411-3-git-send-email-stefanha@redhat.com> In-Reply-To: <1369406295-20411-1-git-send-email-stefanha@redhat.com> References: <1369406295-20411-1-git-send-email-stefanha@redhat.com> Subject: [Qemu-devel] [PATCH 2/2] rtl8139: flush queued packets when RxBufPtr is written List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Anthony Liguori , Stefan Hajnoczi Net queues support efficient "receive disable". For example, tap's file descriptor will not be polled while its peer has receive disabled. This saves CPU cycles for needlessly copying and then dropping packets which the peer cannot receive. rtl8139 is missing the qemu_flush_queued_packets() call that wakes the queue up when receive becomes possible again. As a result, the Windows 7 guest driver reaches a state where the rtl8139 cannot receive packets. The driver has actually refilled the receive buffer but we never resume reception. The bug can be reproduced by running a large FTP 'get' inside a Windows 7 guest: $ qemu -netdev tap,id=tap0,... -device rtl8139,netdev=tap0 The Linux guest driver does not trigger the bug, probably due to a different buffer management strategy. Reported-by: Oliver Francke Signed-off-by: Stefan Hajnoczi --- hw/net/rtl8139.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c index 9369507..7993f9f 100644 --- a/hw/net/rtl8139.c +++ b/hw/net/rtl8139.c @@ -2575,6 +2575,9 @@ static void rtl8139_RxBufPtr_write(RTL8139State *s, uint32_t val) /* this value is off by 16 */ s->RxBufPtr = MOD2(val + 0x10, s->RxBufferSize); + /* more buffer space may be available so try to receive */ + qemu_flush_queued_packets(qemu_get_queue(s->nic)); + DPRINTF(" CAPR write: rx buffer length %d head 0x%04x read 0x%04x\n", s->RxBufferSize, s->RxBufAddr, s->RxBufPtr); } -- 1.8.1.4