On Mon, Oct 17, 2011 at 10:55:57AM +0800, Jason Wang wrote: > Reduce spurious packet drops on RX ring empty when in c+ mode by verifying > that > we have at least 1 buffer ahead of the time. > > Change from v1: > Fix style comments from Stefan. > > Signed-off-by: Jason Wang <jasow...@redhat.com> > --- > hw/rtl8139.c | 44 ++++++++++++++++++++++++++++++-------------- > 1 files changed, 30 insertions(+), 14 deletions(-) > > diff --git a/hw/rtl8139.c b/hw/rtl8139.c > index 3753950..bcbc5e3 100644 > --- a/hw/rtl8139.c > +++ b/hw/rtl8139.c > @@ -84,6 +84,19 @@ > #define VLAN_TCI_LEN 2 > #define VLAN_HLEN (ETHER_TYPE_LEN + VLAN_TCI_LEN) > > +/* w0 ownership flag */ > +#define CP_RX_OWN (1<<31) > +/* w0 end of ring flag */ > +#define CP_RX_EOR (1<<30) > +/* w0 bits 0...12 : buffer size */ > +#define CP_RX_BUFFER_SIZE_MASK ((1<<13) - 1) > +/* w1 tag available flag */ > +#define CP_RX_TAVA (1<<16) > +/* w1 bits 0...15 : VLAN tag */ > +#define CP_RX_VLAN_TAG_MASK ((1<<16) - 1) > +/* w2 low 32bit of Rx buffer ptr */ > +/* w3 high 32bit of Rx buffer ptr */ > + > #if defined (DEBUG_RTL8139) > # define DPRINTF(fmt, ...) \ > do { fprintf(stderr, "RTL8139: " fmt, ## __VA_ARGS__); } while (0) > @@ -805,6 +818,22 @@ static inline target_phys_addr_t rtl8139_addr64(uint32_t > low, uint32_t high) > #endif > } > > +/* Verify that we have at least one available rx buffer */ > +static int rtl8139_cp_has_rxbuf(RTL8139State *s) > +{ > + uint32_t val, rxdw0; > + target_phys_addr_t cplus_rx_ring_desc = rtl8139_addr64(s->RxRingAddrLO, > + s->RxRingAddrHI); > + cplus_rx_ring_desc += 16 * s->currCPlusRxDesc; > + cpu_physical_memory_read(cplus_rx_ring_desc, &val, 4);
Interesting. Please note that cpu_physical_memory_read is not done atomically. Can guest be writing the value while we read it? If yes we'll get a corrupted value here, because CP_RX_OWN is the high bit so it is read last. Correct? I realize we have the same pattern in other places in this device, probably a bug as well? > + rxdw0 = le32_to_cpu(val); > + if (rxdw0 & CP_RX_OWN) { > + return 1; > + } else { > + return 0; > + } Do we need to check that buffer size is large enough to include the packet like we do for non c+ mode? > +} > + > static int rtl8139_can_receive(VLANClientState *nc) > { > RTL8139State *s = DO_UPCAST(NICState, nc, nc)->opaque; > @@ -819,7 +848,7 @@ static int rtl8139_can_receive(VLANClientState *nc) > if (rtl8139_cp_receiver_enabled(s)) { > /* ??? Flow control not implemented in c+ mode. > This is a hack to work around slirp deficiencies anyway. */ > - return 1; > + return rtl8139_cp_has_rxbuf(s); > } else { > avail = MOD2(s->RxBufferSize + s->RxBufPtr - s->RxBufAddr, > s->RxBufferSize); > @@ -965,19 +994,6 @@ static ssize_t rtl8139_do_receive(VLANClientState *nc, > const uint8_t *buf, size_ > > /* begin C+ receiver mode */ > > -/* w0 ownership flag */ > -#define CP_RX_OWN (1<<31) > -/* w0 end of ring flag */ > -#define CP_RX_EOR (1<<30) > -/* w0 bits 0...12 : buffer size */ > -#define CP_RX_BUFFER_SIZE_MASK ((1<<13) - 1) > -/* w1 tag available flag */ > -#define CP_RX_TAVA (1<<16) > -/* w1 bits 0...15 : VLAN tag */ > -#define CP_RX_VLAN_TAG_MASK ((1<<16) - 1) > -/* w2 low 32bit of Rx buffer ptr */ > -/* w3 high 32bit of Rx buffer ptr */ > - > int descriptor = s->currCPlusRxDesc; > target_phys_addr_t cplus_rx_ring_desc; >