From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: [PATCH 7/7] 8139cp: Avoid gratuitous writes to TxPoll register when already running Date: Mon, 21 Sep 2015 15:05:40 +0100 Message-ID: <1442844340.7367.19.camel@infradead.org> References: <1442843991.7367.4.camel@infradead.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-m4qo/7prbzZiFgQ+zMZW" Cc: romieu@fr.zoreil.com To: netdev@vger.kernel.org Return-path: Received: from bombadil.infradead.org ([198.137.202.9]:48818 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932077AbbIUOFo (ORCPT ); Mon, 21 Sep 2015 10:05:44 -0400 In-Reply-To: <1442843991.7367.4.camel@infradead.org> Sender: netdev-owner@vger.kernel.org List-ID: --=-m4qo/7prbzZiFgQ+zMZW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable From: David Woodhouse This is a minor optimisation, but as a side-effect it means we can know precisely which descriptors were already in the ring when we last prodded it to run. This will give us a better chance to catch the case where we get a TxEmpty interrupt when it hasn't actually finished the descriptors we *know* it should have seen, before it ends up being a full-blown TX timeout and reset. Since QEMU's emulation doesn't give TxEmpty interrupts, *always* bash on TxPoll until we see the first TxEmpty interrupt and cp->txempty_seen gets set. Signed-off-by: David Woodhouse --- I'm actually having second thoughts about this one since realising that QEMU doesn't implement it correctly. The workaround isn't *that* horrid but it's not clear it's enough of a performance win =E2=80=94 or whether it= 's entirely necessary for catching my TX stall. drivers/net/ethernet/realtek/8139cp.c | 37 +++++++++++++++++++++++++++++--= ---- 1 file changed, 31 insertions(+), 6 deletions(-) diff --git a/drivers/net/ethernet/realtek/8139cp.c b/drivers/net/ethernet/r= ealtek/8139cp.c index 6feff9f..67a4fcf 100644 --- a/drivers/net/ethernet/realtek/8139cp.c +++ b/drivers/net/ethernet/realtek/8139cp.c @@ -340,6 +340,9 @@ struct cp_private { =20 unsigned tx_head ____cacheline_aligned; unsigned tx_tail; + unsigned tx_running; + unsigned txempty_seen; + struct cp_desc *tx_ring; struct sk_buff *tx_skb[CP_TX_RING_SIZE]; u32 tx_opts[CP_TX_RING_SIZE]; @@ -611,6 +614,22 @@ static irqreturn_t cp_interrupt (int irq, void *dev_in= stance) if (status & (TxOK | TxErr | TxEmpty | SWInt)) handled |=3D cp_tx(cp); =20 + if ((status & TxEmpty) && cp->tx_running) { + handled =3D 1; + /* Qemu's emulation doesn't give TxEmpty interrupts */ + cp->txempty_seen =3D 1; + if (cp->tx_head =3D=3D cp->tx_tail) { + /* Out of descriptors and we have nothing more for it. + Let it stop. */ + cp->tx_running =3D 0; + } else { + /* The hardware raced with us adding a new descriptor, + and we didn't get the TxEmpty IRQ in time so we + didn't prod it. Prod it now to restart. */ + cpw8(TxPoll, NormalTxPoll); + } + } + if (status & LinkChg) { handled =3D 1; mii_check_media(&cp->mii_if, netif_msg_link(cp), false); @@ -796,8 +815,9 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb, =20 cp->tx_skb[entry] =3D skb; cp->tx_opts[entry] =3D flags; - netif_dbg(cp, tx_queued, cp->dev, "tx queued, slot %d, skblen %d\n", - entry, skb->len); + netif_dbg(cp, tx_queued, cp->dev, + "tx queued, slot %d, skblen %d r %d\n", + entry, skb->len, cp->tx_running); } else { struct cp_desc *txd; u32 first_len, first_eor, ctrl; @@ -886,8 +906,9 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb, wmb(); =20 cp->tx_opts[first_entry] =3D ctrl; - netif_dbg(cp, tx_queued, cp->dev, "tx queued, slots %d-%d, skblen %d\n", - first_entry, entry, skb->len); + netif_dbg(cp, tx_queued, cp->dev, + "tx queued, slots %d-%d, skblen %d r %d\n", + first_entry, entry, skb->len, cp->tx_running); } cp->tx_head =3D NEXT_TX(entry); =20 @@ -895,11 +916,13 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb= , if (TX_BUFFS_AVAIL(cp) <=3D (MAX_SKB_FRAGS + 1)) netif_stop_queue(dev); =20 + if (!cp->tx_running || !cp->txempty_seen) { + cpw8(TxPoll, NormalTxPoll); + cp->tx_running =3D 1; + } out_unlock: spin_unlock_irqrestore(&cp->lock, intr_flags); =20 - cpw8(TxPoll, NormalTxPoll); - return NETDEV_TX_OK; out_dma_error: dev_kfree_skb_any(skb); @@ -989,6 +1012,7 @@ static void cp_stop_hw (struct cp_private *cp) =20 cp->rx_tail =3D 0; cp->tx_head =3D cp->tx_tail =3D 0; + cp->tx_running =3D 0; =20 netdev_reset_queue(cp->dev); } @@ -1041,6 +1065,7 @@ static inline void cp_start_hw (struct cp_private *cp= ) * This variant appears to work fine. */ cpw8(Cmd, RxOn | TxOn); + cp->tx_running =3D 0; =20 netdev_reset_queue(cp->dev); } --=20 2.4.3 --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-m4qo/7prbzZiFgQ+zMZW Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; 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