Date: Thu, 11 Jun 2009 05:20:05 +0000 (UTC) From: Kip Macy <kmacy@FreeBSD.org> To: src-committers@freebsd.org, svn-src-user@freebsd.org Subject: svn commit: r193968 - user/kmacy/releng_7_2_xen/sys/dev/xen/netfront Message-ID: <200906110520.n5B5K5xT036280@svn.freebsd.org>
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Author: kmacy Date: Thu Jun 11 05:20:05 2009 New Revision: 193968 URL: http://svn.freebsd.org/changeset/base/193968 Log: integrate 19286-192870 Modified: user/kmacy/releng_7_2_xen/sys/dev/xen/netfront/netfront.c Modified: user/kmacy/releng_7_2_xen/sys/dev/xen/netfront/netfront.c ============================================================================== --- user/kmacy/releng_7_2_xen/sys/dev/xen/netfront/netfront.c Thu Jun 11 04:50:11 2009 (r193967) +++ user/kmacy/releng_7_2_xen/sys/dev/xen/netfront/netfront.c Thu Jun 11 05:20:05 2009 (r193968) @@ -284,6 +284,7 @@ struct netfront_rx_info { static inline void add_id_to_freelist(struct mbuf **list, unsigned short id) { + KASSERT(id != 0, ("add_id_to_freelist: the head item (0) must always be free.")); list[id] = list[0]; list[0] = (void *)(u_long)id; } @@ -292,6 +293,7 @@ static inline unsigned short get_id_from_freelist(struct mbuf **list) { u_int id = (u_int)(u_long)list[0]; + KASSERT(id != 0, ("get_id_from_freelist: the head item (0) must always remain free.")); list[0] = list[id]; return (id); } @@ -658,6 +660,23 @@ xn_free_tx_ring(struct netfront_info *sc #endif } +/* + * Do some brief math on the number of descriptors available to + * determine how many slots are available. + * + * Firstly - wouldn't something with RING_FREE_REQUESTS() be more applicable? + * Secondly - MAX_SKB_FRAGS is a Linux construct which may not apply here. + * Thirdly - it isn't used here anyway; the magic constant '24' is possibly + * wrong? + * The "2" is presumably to ensure there are also enough slots available for + * the ring entries used for "options" (eg, the TSO entry before a packet + * is queued); I'm not sure why its 2 and not 1. Perhaps to make sure there's + * a "free" node in the tx mbuf list (node 0) to represent the freelist? + * + * This only figures out whether any xenbus ring descriptors are available; + * it doesn't at all reflect how many tx mbuf ring descriptors are also + * available. + */ static inline int netfront_tx_slot_available(struct netfront_info *np) { @@ -990,10 +1009,10 @@ xn_txeof(struct netfront_info *np) for (i = np->tx.rsp_cons; i != prod; i++) { id = RING_GET_RESPONSE(&np->tx, i)->id; m = np->xn_cdata.xn_tx_chain[id]; - - ifp->if_opackets++; KASSERT(m != NULL, ("mbuf not found in xn_tx_chain")); M_ASSERTVALID(m); + + ifp->if_opackets++; if (unlikely(gnttab_query_foreign_access( np->grant_tx_ref[id]) != 0)) { printf("network_tx_buf_gc: warning " @@ -1325,6 +1344,12 @@ xn_start_locked(struct ifnet *ifp) if (m_head == NULL) break; + /* + * netfront_tx_slot_available() tries to do some math to + * ensure that there'll be enough xenbus ring slots available + * for the maximum number of packet fragments (and a couple more + * for what I guess are TSO and other ring entry items.) + */ if (!netfront_tx_slot_available(sc)) { IF_PREPEND(&ifp->if_snd, m_head); ifp->if_drv_flags |= IFF_DRV_OACTIVE;
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