From 339cf6d409598e52f5958c9a0941337281da90db Mon Sep 17 00:00:00 2001
From: Xiao Wang <jasowang@redhat.com>
Date: Tue, 24 May 2011 08:35:21 -0300
Subject: [PATCH 1/2] e1000: introduce a helper to check the size of available rx buffers

RH-Author: Xiao Wang <jasowang@redhat.com>
Message-id: <20110524083521.21571.43279.stgit@dhcp-8-149.nay.redhat.com>
Patchwork-id: 25390
O-Subject: [RHEL5.7 V2 PATCH 1/2] e1000: introduce a helper to check the size of available rx buffers
Bugzilla: 704097
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
RH-Acked-by: Markus Armbruster <armbru@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>

A helper was introduced to check the size of available rx buffer size. This
would help reducing packet drop and also for the future support of multiple
descriptors.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=704097

Upstream:
e1000_has_rxbufs() was originally introduced in
322fd48afbed1ef7b834ac343a0c8687bcb33695. Since we only have single descriptor
support for RHEL5 now, the call in e1000_recevie() which is used to avoid
rolling back multiple descriptors is not needed.

Test status: Tested with my local machine

Changed from v1:
- Separated into two patches based on Jes and Markus comments
- s/opaque/s/ and add explain about why just pick e1000_has_rxbuf() in the
  commit log based on Juan's comment.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 qemu/hw/e1000.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/hw/e1000.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/qemu/hw/e1000.c b/qemu/hw/e1000.c
index 1390f5a..dc17736 100644
--- a/qemu/hw/e1000.c
+++ b/qemu/hw/e1000.c
@@ -607,6 +607,24 @@ e1000_set_link_status(VLANClientState *vc)
         set_ics(s, 0, E1000_ICR_LSC);
 }
 
+static int e1000_has_rxbufs(E1000State *s, size_t total_size)
+{
+    int bufs;
+    /* Fast-path short packets */
+    if (total_size <= s->rxbuf_size) {
+        return s->mac_reg[RDH] != s->mac_reg[RDT] || !s->check_rxov;
+    }
+    if (s->mac_reg[RDH] < s->mac_reg[RDT]) {
+        bufs = s->mac_reg[RDT] - s->mac_reg[RDH];
+    } else if (s->mac_reg[RDH] > s->mac_reg[RDT] || !s->check_rxov) {
+        bufs = s->mac_reg[RDLEN] /  sizeof(struct e1000_rx_desc) +
+            s->mac_reg[RDT] - s->mac_reg[RDH];
+    } else {
+	return 0;
+    }
+    return total_size <= bufs * s->rxbuf_size;
+}
+
 static int
 e1000_can_receive(void *opaque)
 {
-- 
1.7.3.2