[src/trunk]: src/sys/dev/pci actually writing always the checksum offload con...

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

details:   https://anonhg.NetBSD.org/src/rev/05286ff881c2
branches:  trunk
changeset: 930579:05286ff881c2
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Wed Apr 08 21:51:42 2020 +0000

description:
actually writing always the checksum offload context descriptor
makes the hw do extra processing, avoid doing that if possible -
on my computer with I219 this results in about 2% speedup in Tx performance

change adoped from FreeBSD

XXX should be also done for multiqueue case, but I don't have hw to test it

diffstat:

 sys/dev/pci/if_wm.c |  61 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 files changed, 53 insertions(+), 8 deletions(-)

diffs (135 lines):

diff -r c7dda7f79aaf -r 05286ff881c2 sys/dev/pci/if_wm.c
--- a/sys/dev/pci/if_wm.c       Wed Apr 08 15:27:18 2020 +0000
+++ b/sys/dev/pci/if_wm.c       Wed Apr 08 21:51:42 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: if_wm.c,v 1.670 2020/03/21 16:47:05 thorpej Exp $      */
+/*     $NetBSD: if_wm.c,v 1.671 2020/04/08 21:51:42 jdolecek Exp $     */
 
 /*
  * Copyright (c) 2001, 2002, 2003, 2004 Wasabi Systems, Inc.
@@ -82,7 +82,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_wm.c,v 1.670 2020/03/21 16:47:05 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_wm.c,v 1.671 2020/04/08 21:51:42 jdolecek Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_net_mpsafe.h"
@@ -379,6 +379,12 @@
        bool txq_sending;
        time_t txq_lastsent;
 
+       /* Checksum flags used for previous packet */
+       uint32_t        txq_last_hw_cmd;
+       uint8_t         txq_last_hw_fields;
+       uint16_t        txq_last_hw_ipcs;
+       uint16_t        txq_last_hw_tucs;
+
        uint32_t txq_packets;           /* for AIM */
        uint32_t txq_bytes;             /* for AIM */
 #ifdef WM_EVENT_COUNTERS
@@ -403,6 +409,7 @@
        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 */
+       WM_Q_EVCNT_DEFINE(txq, skipcontext) /* Tx skip wring cksum context */
 
        char txq_txseg_evcnt_names[WM_NTXSEGS][sizeof("txqXXtxsegXXX")];
        struct evcnt txq_ev_txseg[WM_NTXSEGS]; /* Tx packets w/ N segments */
@@ -6947,6 +6954,7 @@
                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);
+               WM_Q_MISC_EVCNT_ATTACH(txq, skipcontext, txq, i, xname);
 #endif /* WM_EVENT_COUNTERS */
 
                tx_done++;
@@ -7079,6 +7087,7 @@
                WM_Q_EVCNT_DETACH(txq, toomanyseg, txq, i);
                WM_Q_EVCNT_DETACH(txq, defrag, txq, i);
                WM_Q_EVCNT_DETACH(txq, underrun, txq, i);
+               WM_Q_EVCNT_DETACH(txq, skipcontext, txq, i);
 #endif /* WM_EVENT_COUNTERS */
 
                /* Drain txq_interq */
@@ -7394,6 +7403,9 @@
 
        default:
                /* Don't support this protocol or encapsulation. */
+               txq->txq_last_hw_cmd = txq->last_hw_fields = 0;
+               txq->txq_last_hw_ipcs = 0;
+               txq->txq_last_hw_tucs = 0;
                *fieldsp = 0;
                *cmdp = 0;
                return 0;
@@ -7533,13 +7545,47 @@
                    WTX_TCPIP_TUCSE(0) /* Rest of packet */;
        }
 
+       *cmdp = cmd;
+       *fieldsp = fields;
+
        /*
         * We don't have to write context descriptor for every packet
         * except for 82574. For 82574, we must write context descriptor
         * for every packet when we use two descriptor queues.
-        * It would be overhead to write context descriptor for every packet,
-        * however it does not cause problems.
-        */
+        *
+        * The 82574L can only remember the *last* context used
+        * regardless of queue that it was use for.  We cannot reuse
+        * contexts on this hardware platform and must generate a new
+        * context every time.  82574L hardware spec, section 7.2.6,
+        * second note.
+        *
+        * Setting up new checksum offload context for every
+        * frames takes a lot of processing time for hardware.
+        * This also reduces performance a lot for small sized
+        * frames so avoid it if driver can use previously
+        * configured checksum offload context.
+        * For TSO, in theory we can use the same TSO context if and only if
+        * frame is the same type(IP/TCP) and the same MSS. However
+        * checking whether a frame has the same IP/TCP structure is
+        * hard thing so just ignore that and always restablish a
+        * new TSO context.
+        */
+       KASSERT(!wm_is_using_multiqueue(sc));
+       if ((m0->m_pkthdr.csum_flags & (M_CSUM_TSOv4 | M_CSUM_TSOv6)) == 0) {
+               if (txq->txq_last_hw_cmd == cmd &&
+                   txq->txq_last_hw_fields == fields &&
+                   txq->txq_last_hw_ipcs == (ipcs & 0xffff) &&
+                   txq->txq_last_hw_tucs == (tucs & 0xffff)) {
+                       WM_Q_EVCNT_INCR(txq, skipcontext);
+                       return 0;
+               }
+       }
+
+       txq->txq_last_hw_cmd = cmd;
+       txq->txq_last_hw_fields = fields;
+       txq->txq_last_hw_ipcs = (ipcs & 0xffff);
+       txq->txq_last_hw_tucs = (tucs & 0xffff);
+
        /* Fill in the context descriptor. */
        t = (struct livengood_tcpip_ctxdesc *)
            &txq->txq_descs[txq->txq_next];
@@ -7552,9 +7598,6 @@
        txq->txq_next = WM_NEXTTX(txq, txq->txq_next);
        txs->txs_ndesc++;
 
-       *cmdp = cmd;
-       *fieldsp = fields;
-
        return 0;
 }
 
@@ -7839,6 +7882,8 @@
                                continue;
                        }
                } else {
+                       txq->txq_last_hw_cmd = txq->last_hw_fields = 0;
+                       txq->txq_last_hw_ipcs = txq->last_hw_tucs = 0;
                        cksumcmd = 0;
                        cksumfields = 0;
                }