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iflib: netmap: publish all the receive buffer

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At initialization time, the netmap RX refill function used to
prepare the NIC RX ring with N-1 buffers rather than N (with
N equal to the number of descriptors in the NIC RX ring).
This is not how netmap is supposed to work, as it would keep
kring->nr_hwcur not in sync with the NIC "next index to refill"
(i.e., fl->ifl_pidx). Instead we prepare N buffers, although we
still publish (with isc_rxd_flush()) only the first N-1 buffers,
to avoid the NIC producer pointer to overrun the NIC consumer
pointer (for NICs where this is a real issue, e.g. Intel ones).

MFC after:	2 weeks
This commit is contained in:
Vincenzo Maffione 2020-08-25 15:19:45 +00:00
parent a459a6cfe7
commit ae750d5cdf
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=364770
1 changed files with 28 additions and 22 deletions
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50
sys/net/iflib.c
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@ -832,7 +832,6 @@ netmap_fl_refill(iflib_rxq_t rxq, struct netmap_kring *kring, bool init)
{
struct netmap_adapter *na = kring->na;
u_int const lim = kring->nkr_num_slots - 1;
u_int head = kring->rhead;
u_int nm_i = kring->nr_hwcur;
struct netmap_ring *ring = kring->ring;
bus_dmamap_t *map;
@ -840,39 +839,46 @@ netmap_fl_refill(iflib_rxq_t rxq, struct netmap_kring *kring, bool init)
if_ctx_t ctx = rxq->ifr_ctx;
iflib_fl_t fl = &rxq->ifr_fl[0];
u_int nic_i_first, nic_i;
int i;
int i, n;
#if IFLIB_DEBUG_COUNTERS
int rf_count = 0;
#endif
/*
* Netmap requires that we leave (at least) one free slot
* in the ring, so that it can distinguish between an empty
* ring (nr_hwcur == nr_hwtail, i.e. all the buffers owned by the
* user) and a full ring (nr_hwtail == (nr_hwcur - 1) mod N, i.e.
* all the buffers owned by the kernel).
* We thus set head (the refill limit) to nr_hwcur - 1
* at initialization. The rest of the code will then make sure
* than nr_hwtail never overcomes nr_hwcur.
* This function is used both at initialization and in rxsync.
* At initialization we need to prepare (with isc_rxd_refill())
* all the (N) netmap buffers in the ring, in such a way to keep
* fl->ifl_pidx and kring->nr_hwcur in sync (except for
* kring->nkr_hwofs); at rxsync time, both indexes point to the
* next buffer to be refilled.
* In any case we publish (with isc_rxd_flush()) up to
* (fl->ifl_pidx - 1) % N (included), to avoid the NIC tail/prod
* pointer to overrun the head/cons pointer, although this is
* not necessary for some NICs (e.g. vmx).
*/
if (__predict_false(init)) {
head = nm_prev(nm_i, lim);
} else if (nm_i == head) {
/* Nothing to do. We can leave early. */
return (0);
if (__predict_false(init))
n = kring->nkr_num_slots;
else {
n = kring->rhead - nm_i;
if (n == 0)
return (0); /* Nothing to do. */
if (n < 0)
n += kring->nkr_num_slots;
}
/* Start to refill from nr_hwcur, publishing n buffers. */
iru_init(&iru, rxq, 0 /* flid */);
map = fl->ifl_sds.ifsd_map;
nic_i = netmap_idx_k2n(kring, nm_i);
nic_i = fl->ifl_pidx;
MPASS(nic_i == netmap_idx_k2n(kring, nm_i));
DBG_COUNTER_INC(fl_refills);
while (nm_i != head) {
while (n > 0) {
#if IFLIB_DEBUG_COUNTERS
if (++rf_count == 9)
DBG_COUNTER_INC(fl_refills_large);
#endif
nic_i_first = nic_i;
for (i = 0; i < IFLIB_MAX_RX_REFRESH && nm_i != head; i++) {
for (i = 0; n > 0 && i < IFLIB_MAX_RX_REFRESH; n--, i++) {
struct netmap_slot *slot = &ring->slot[nm_i];
void *addr = PNMB(na, slot, &fl->ifl_bus_addrs[i]);
@ -903,11 +909,11 @@ netmap_fl_refill(iflib_rxq_t rxq, struct netmap_kring *kring, bool init)
iru.iru_count = i;
ctx->isc_rxd_refill(ctx->ifc_softc, &iru);
}
kring->nr_hwcur = head;
fl->ifl_pidx = nic_i;
MPASS(!init || nm_i == 0);
MPASS(nm_i == kring->rhead);
kring->nr_hwcur = nm_i;
/* The pidx argument of isc_rxd_flush() is the index of the last valid
* slot in the free list ring. We need therefore to decrement nic_i,
* similarly to what happens in iflib_fl_refill() for ifl_pidx. */
bus_dmamap_sync(fl->ifl_ifdi->idi_tag, fl->ifl_ifdi->idi_map,
BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE);
ctx->isc_rxd_flush(ctx->ifc_softc, rxq->ifr_id, fl->ifl_id,