[src/trunk]: src/sys/dev/pci - Try m_defrag() to reduce the number of DMA seg...

[msaitoh <msaitoh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/49cc7a24542f
branches:  trunk
changeset: 835827:49cc7a24542f
user:      msaitoh <msaitoh%NetBSD.org@localhost>
date:      Wed Sep 12 04:59:26 2018 +0000

description:
- Try m_defrag() to reduce the number of DMA segment if bus_dmamap_load_mbuf()
  returned EFBIG. When m_defrag() is called, txqNNdefrag event counter is
  incremented. If the 2nd try of bus_dmamap_load_mbuf() failed, txqNNtoomanyseg
  event counter is incremented.

- Reduce the max number of DMA segemts from 256 to 64 (it's the same valuse
  as other BSD's (EM_MAX_SCATTER) and more than before if_wm.c rev. 1.75's
  value (40)) because we do m_defrag() now.

diffstat:

 sys/dev/pci/if_wm.c |  56 ++++++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 45 insertions(+), 11 deletions(-)

diffs (133 lines):

diff -r fea5b66a3be2 -r 49cc7a24542f sys/dev/pci/if_wm.c
--- a/sys/dev/pci/if_wm.c       Wed Sep 12 04:37:18 2018 +0000
+++ b/sys/dev/pci/if_wm.c       Wed Sep 12 04:59:26 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: if_wm.c,v 1.586 2018/09/12 04:37:18 msaitoh Exp $      */
+/*     $NetBSD: if_wm.c,v 1.587 2018/09/12 04:59:26 msaitoh Exp $      */
 
 /*
  * Copyright (c) 2001, 2002, 2003, 2004 Wasabi Systems, Inc.
@@ -83,7 +83,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_wm.c,v 1.586 2018/09/12 04:37:18 msaitoh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_wm.c,v 1.587 2018/09/12 04:59:26 msaitoh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_net_mpsafe.h"
@@ -197,11 +197,12 @@
  * of packets, and we go ahead and manage up to 64 (16 for the i82547)
  * of them at a time.
  *
- * We allow up to 256 (!) DMA segments per packet.  Pathological packet
+ * We allow up to 64 DMA segments per packet.  Pathological packet
  * chains containing many small mbufs have been observed in zero-copy
- * situations with jumbo frames.
- */
-#define        WM_NTXSEGS              256
+ * situations with jumbo frames. If a mbuf chain has more than 40 DMA segments,
+ * m_defrag() is called to reduce it.
+ */
+#define        WM_NTXSEGS              64
 #define        WM_IFQUEUELEN           256
 #define        WM_TXQUEUELEN_MAX       64
 #define        WM_TXQUEUELEN_MAX_82547 16
@@ -392,7 +393,10 @@
        WM_Q_EVCNT_DEFINE(txq, tsopain)     /* Painful header manip. for TSO */
        WM_Q_EVCNT_DEFINE(txq, pcqdrop)     /* Pkt dropped in pcq */
        WM_Q_EVCNT_DEFINE(txq, descdrop)    /* Pkt dropped in MAC desc ring */
-
+                                           /* other than toomanyseg */
+
+       WM_Q_EVCNT_DEFINE(txq, toomanyseg)  /* Pkt dropped(toomany DMA segs) */
+       WM_Q_EVCNT_DEFINE(txq, defrag)      /* m_defrag() */
        WM_Q_EVCNT_DEFINE(txq, underrun)    /* Tx underrun */
 
        char txq_txseg_evcnt_names[WM_NTXSEGS][sizeof("txqXXtxsegXXX")];
@@ -6472,6 +6476,8 @@
 
                WM_Q_MISC_EVCNT_ATTACH(txq, pcqdrop, txq, i, xname);
                WM_Q_MISC_EVCNT_ATTACH(txq, descdrop, txq, i, xname);
+               WM_Q_MISC_EVCNT_ATTACH(txq, toomanyseg, txq, i, xname);
+               WM_Q_MISC_EVCNT_ATTACH(txq, defrag, txq, i, xname);
                WM_Q_MISC_EVCNT_ATTACH(txq, underrun, txq, i, xname);
 #endif /* WM_EVENT_COUNTERS */
 
@@ -6592,6 +6598,8 @@
 
                WM_Q_EVCNT_DETACH(txq, pcqdrop, txq, i);
                WM_Q_EVCNT_DETACH(txq, descdrop, txq, i);
+               WM_Q_EVCNT_DETACH(txq, toomanyseg, txq, i);
+               WM_Q_EVCNT_DETACH(txq, defrag, txq, i);
                WM_Q_EVCNT_DETACH(txq, underrun, txq, i);
 #endif /* WM_EVENT_COUNTERS */
 
@@ -7173,6 +7181,7 @@
        bus_size_t seglen, curlen;
        uint32_t cksumcmd;
        uint8_t cksumfields;
+       bool remap = true;
 
        KASSERT(mutex_owned(txq->txq_lock));
 
@@ -7246,11 +7255,23 @@
                 * since we can't sanely copy a jumbo packet to a single
                 * buffer.
                 */
+retry:
                error = bus_dmamap_load_mbuf(sc->sc_dmat, dmamap, m0,
                    BUS_DMA_WRITE | BUS_DMA_NOWAIT);
-               if (error) {
+               if (__predict_false(error)) {
                        if (error == EFBIG) {
-                               WM_Q_EVCNT_INCR(txq, descdrop);
+                               if (remap == true) {
+                                       struct mbuf *m;
+
+                                       remap = false;
+                                       m = m_defrag(m0, M_NOWAIT);
+                                       if (m != NULL) {
+                                               WM_Q_EVCNT_INCR(txq, defrag);
+                                               m0 = m;
+                                               goto retry;
+                                       }
+                               }
+                               WM_Q_EVCNT_INCR(txq, toomanyseg);
                                log(LOG_ERR, "%s: Tx packet consumes too many "
                                    "DMA segments, dropping...\n",
                                    device_xname(sc->sc_dev));
@@ -7775,6 +7796,7 @@
        bus_dmamap_t dmamap;
        int error, nexttx, lasttx = -1, seg, segs_needed;
        bool do_csum, sent;
+       bool remap = true;
 
        KASSERT(mutex_owned(txq->txq_lock));
 
@@ -7830,11 +7852,23 @@
                 * since we can't sanely copy a jumbo packet to a single
                 * buffer.
                 */
+retry:
                error = bus_dmamap_load_mbuf(sc->sc_dmat, dmamap, m0,
                    BUS_DMA_WRITE | BUS_DMA_NOWAIT);
-               if (error) {
+               if (__predict_false(error)) {
                        if (error == EFBIG) {
-                               WM_Q_EVCNT_INCR(txq, descdrop);
+                               if (remap == true) {
+                                       struct mbuf *m;
+
+                                       remap = false;
+                                       m = m_defrag(m0, M_NOWAIT);
+                                       if (m != NULL) {
+                                               WM_Q_EVCNT_INCR(txq, defrag);
+                                               m0 = m;
+                                               goto retry;
+                                       }
+                               }
+                               WM_Q_EVCNT_INCR(txq, toomanyseg);
                                log(LOG_ERR, "%s: Tx packet consumes too many "
                                    "DMA segments, dropping...\n",
                                    device_xname(sc->sc_dev));