From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:43384) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h14Fj-0002gz-Cr for qemu-devel@nongnu.org; Tue, 05 Mar 2019 02:12:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h14Fi-0000b2-H2 for qemu-devel@nongnu.org; Tue, 05 Mar 2019 02:12:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46422) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h14Fg-0000ZT-KJ for qemu-devel@nongnu.org; Tue, 05 Mar 2019 02:12:36 -0500 From: Jason Wang Date: Tue, 5 Mar 2019 15:12:11 +0800 Message-Id: <1551769940-22739-5-git-send-email-jasowang@redhat.com> In-Reply-To: <1551769940-22739-1-git-send-email-jasowang@redhat.com> References: <1551769940-22739-1-git-send-email-jasowang@redhat.com> Subject: [Qemu-devel] [PULL V2 04/13] net: netmap: improve netmap_receive_iov() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, peter.maydell@linaro.org Cc: Vincenzo Maffione , Jason Wang From: Vincenzo Maffione Changes: - Save CPU cycles by computing the return value while scanning the input iovec, rather than calling iov_size() at the end. - Remove check for s->tx != NULL, because it cannot happen. - Cache ring->tail in a local variable and use it to check for space in the TX ring. The use of nm_ring_empty() was invalid, because nobody is updating ring->cur and ring->head at that point. - In case we run out of netmap slots in the middle of a packet, move the wake-up point by advancing ring->cur, but do not expose the incomplete packet (i.e., by updating also ring->head). Signed-off-by: Vincenzo Maffione Signed-off-by: Jason Wang --- net/netmap.c | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-) diff --git a/net/netmap.c b/net/netmap.c index 852106a..0cc8f54 100644 --- a/net/netmap.c +++ b/net/netmap.c @@ -159,21 +159,22 @@ static ssize_t netmap_receive_iov(NetClientState *nc, { NetmapState *s = DO_UPCAST(NetmapState, nc, nc); struct netmap_ring *ring = s->tx; + unsigned int tail = ring->tail; + ssize_t totlen = 0; uint32_t last; uint32_t idx; uint8_t *dst; int j; uint32_t i; - if (unlikely(!ring)) { - /* Drop the packet. */ - return iov_size(iov, iovcnt); - } - - last = i = ring->cur; + last = i = ring->head; if (nm_ring_space(ring) < iovcnt) { - /* Not enough netmap slots. */ + /* Not enough netmap slots. Tell the kernel that we have seen the new + * available slots (so that it notifies us again when it has more + * ones), but without publishing any new slots to be processed + * (e.g., we don't advance ring->head). */ + ring->cur = tail; netmap_write_poll(s, true); return 0; } @@ -183,14 +184,17 @@ static ssize_t netmap_receive_iov(NetClientState *nc, int offset = 0; int nm_frag_size; + totlen += iov_frag_size; + /* Split each iovec fragment over more netmap slots, if necessary. */ while (iov_frag_size) { nm_frag_size = MIN(iov_frag_size, ring->nr_buf_size); - if (unlikely(nm_ring_empty(ring))) { - /* We run out of netmap slots while splitting the + if (unlikely(i == tail)) { + /* We ran out of netmap slots while splitting the iovec fragments. */ + ring->cur = tail; netmap_write_poll(s, true); return 0; } @@ -212,12 +216,13 @@ static ssize_t netmap_receive_iov(NetClientState *nc, /* The last slot must not have NS_MOREFRAG set. */ ring->slot[last].flags &= ~NS_MOREFRAG; - /* Now update ring->cur and ring->head. */ - ring->cur = ring->head = i; + /* Now update ring->head and ring->cur to publish the new slots and + * the new wakeup point. */ + ring->head = ring->cur = i; ioctl(s->nmd->fd, NIOCTXSYNC, NULL); - return iov_size(iov, iovcnt); + return totlen; } static ssize_t netmap_receive(NetClientState *nc, -- 2.5.0