From e3ef7bb21608dd77fae2ac9790b12f3ea9ebe541 Mon Sep 17 00:00:00 2001 From: Andrew Rybchenko Date: Tue, 10 Jan 2017 16:25:39 +0000 Subject: [PATCH] sfxge(4): avoid unnecessary mbuf data prefetch Unnecessary prefetch just loads HW prefetcher and displaces other cache entries (which could be really useful). If we parse mbuf for TSO early and use firmware-assisted TSO, we do not expect mbuf data access when we compose firmware-assisted TSO (v1 or v2) option descriptors. If packet header needs to be linearized or finally FATSO cannot be used because of, for example, too big header, we do not care about a bit more performance degradation because of prefetch absence (it is better to optimize more common case). Reviewed by: gnn Sponsored by: Solarflare Communications, Inc. MFC after: 2 days Differential Revision: https://reviews.freebsd.org/D9120 --- sys/dev/sfxge/sfxge_tx.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/sys/dev/sfxge/sfxge_tx.c b/sys/dev/sfxge/sfxge_tx.c index 4e31aeccbb2..dd78e6e8a24 100644 --- a/sys/dev/sfxge/sfxge_tx.c +++ b/sys/dev/sfxge/sfxge_tx.c @@ -363,8 +363,22 @@ static int sfxge_tx_queue_mbuf(struct sfxge_txq *txq, struct mbuf *mbuf) KASSERT(!txq->blocked, ("txq->blocked")); +#if SFXGE_TX_PARSE_EARLY + /* + * If software TSO is used, we still need to copy packet header, + * even if we have already parsed it early before enqueue. + */ + if ((mbuf->m_pkthdr.csum_flags & CSUM_TSO) && + (txq->tso_fw_assisted == 0)) + prefetch_read_many(mbuf->m_data); +#else + /* + * Prefetch packet header since we need to parse it and extract + * IP ID, TCP sequence number and flags. + */ if (mbuf->m_pkthdr.csum_flags & CSUM_TSO) prefetch_read_many(mbuf->m_data); +#endif if (__predict_false(txq->init_state != SFXGE_TXQ_STARTED)) { rc = EINTR;