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Message-Id: <1210059485-691-5-git-send-email-gerrit@erg.abdn.ac.uk>
Date: Tue, 6 May 2008 08:38:05 +0100
From: Gerrit Renker <gerrit@....abdn.ac.uk>
To: acme@...hat.com
Cc: dccp@...r.kernel.org, netdev@...r.kernel.org,
Gerrit Renker <gerrit@....abdn.ac.uk>
Subject: [PATCH 4/4] [CCID-3]: Remove indirection when parsing options
The `options_received' struct is redundant, since it re-duplicates the existing
`p' and `x_recv' fields. This patch removes the sub-struct and migrates the
related format conversion operations (cf. below) to ccid3_hc_tx_parse_options().
The patch also adds a convenience function to convert a reciprocal value into
the loss rate p, performing the scaling and considering the two special cases:
* 1/(2^32-1) is mapped into 0% as per RFC 4342, 8.5;
* 1/0 is mapped into the maximum of 100%.
This further fixes a bug in ccid3_hc_rx_getsockopt (1/0 was mapped into ~0U),
which now allows to consistently print the scaled p-values as
printf("Loss Event Rate = %u.%04u %%\n", rx_info.tfrcrx_p / 10000,
rx_info.tfrcrx_p % 10000);
Lastly, documentation about the scaling factor used for fractions was added.
----------------------------------------------
Why the fields are redundant [can be removed]
----------------------------------------------
The Loss Event Rate p and the Receive Rate x_recv are initially 0 when first
loading CCID-3, as ccid_new() zeroes out the entire ccid3_hc_tx_sock.
When Loss Event Rate or Receive Rate options are received, they are stored by
ccid3_hc_tx_parse_options() into the fields `ccid3or_loss_event_rate' and
`ccid3or_receive_rate' of the sub-struct `options_received' in ccid3_hc_tx_sock.
After parsing (considering only the established state - dccp_rcv_established()),
the packet is passed on to ccid_hc_tx_packet_recv(). This calls the CCID-3
specific routine ccid3_hc_tx_packet_recv(), which performs the following copy
operations between fields of ccid3_hc_tx_sock:
* hctx->options_received.ccid3or_receive_rate is copied into hctx->x_recv,
after scaling it for fixpoint arithmetic, by 2^64;
* hctx->options_received.ccid3or_loss_event_rate is copied into hctx->p,
considering the above special cases; in addition, a value of 0 here needs to
be mapped into p=0 (when no Loss Event Rate option has been received yet).
Signed-off-by: Gerrit Renker <gerrit@....abdn.ac.uk>
---
net/dccp/ccids/ccid3.c | 27 +++++++++------------------
net/dccp/ccids/ccid3.h | 9 +--------
net/dccp/ccids/lib/tfrc.h | 26 ++++++++++++++++++++++++--
3 files changed, 34 insertions(+), 28 deletions(-)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -366,11 +366,10 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, unsigned int len)
static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
{
struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
- struct ccid3_options_received *opt_recv = &hctx->options_received;
struct tfrc_tx_hist_entry *acked;
ktime_t now;
unsigned long t_nfb;
- u32 pinv, r_sample;
+ u32 r_sample;
/* we are only interested in ACKs */
if (!(DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK ||
@@ -395,17 +394,6 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
r_sample = dccp_sample_rtt(sk, ktime_us_delta(now, acked->stamp));
hctx->rtt = tfrc_ewma(hctx->rtt, r_sample, 9);
- /* Update receive rate in units of 64 * bytes/second */
- hctx->x_recv = opt_recv->ccid3or_receive_rate;
- hctx->x_recv <<= 6;
-
- /* Update loss event rate (which is scaled by 1e6) */
- pinv = opt_recv->ccid3or_loss_event_rate;
- if (pinv == ~0U || pinv == 0) /* see RFC 4342, 8.5 */
- hctx->p = 0;
- else /* can not exceed 100% */
- hctx->p = scaled_div(1, pinv);
-
/*
* Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
*/
@@ -478,7 +466,6 @@ static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
u8 option, u8 *optval, u8 optlen)
{
struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
- struct ccid3_options_received *opt_recv = &hctx->options_received;
__be32 opt_val;
switch (option) {
@@ -495,11 +482,16 @@ static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
opt_val = ntohl(get_unaligned((__be32 *)optval));
if (option == TFRC_OPT_RECEIVE_RATE) {
- opt_recv->ccid3or_receive_rate = opt_val;
+ /* Receive Rate is kept in units of 64 bytes/second */
+ hctx->x_recv = opt_val;
+ hctx->x_recv <<= 6;
+
ccid3_pr_debug("%s(%p), RECEIVE_RATE=%u\n",
dccp_role(sk), sk, opt_val);
} else {
- opt_recv->ccid3or_loss_event_rate = opt_val;
+ /* Update the fixpoint Loss Event Rate fraction */
+ hctx->p = tfrc_invert_loss_rate(opt_val);
+
ccid3_pr_debug("%s(%p), LOSS_EVENT_RATE=%u\n",
dccp_role(sk), sk, opt_val);
}
@@ -836,8 +828,7 @@ static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len,
return -EINVAL;
rx_info.tfrcrx_x_recv = hcrx->x_recv;
rx_info.tfrcrx_rtt = hcrx->rtt;
- rx_info.tfrcrx_p = hcrx->p_inverse == 0 ? ~0U :
- scaled_div(1, hcrx->p_inverse);
+ rx_info.tfrcrx_p = tfrc_invert_loss_rate(hcrx->p_inverse);
len = sizeof(rx_info);
val = &rx_info;
break;
--- a/net/dccp/ccids/ccid3.h
+++ b/net/dccp/ccids/ccid3.h
@@ -59,11 +59,6 @@ enum ccid3_options {
TFRC_OPT_RECEIVE_RATE = 194,
};
-struct ccid3_options_received {
- u32 ccid3or_loss_event_rate;
- u32 ccid3or_receive_rate;
-};
-
/* TFRC sender states */
enum ccid3_hc_tx_states {
TFRC_SSTATE_NO_SENT = 1,
@@ -77,7 +72,7 @@ enum ccid3_hc_tx_states {
* @x_recv - Receive rate in 64 * bytes per second
* @x_calc - Calculated rate in bytes per second
* @rtt - Estimate of current round trip time in usecs
- * @p - Current loss event rate (0-1) scaled by 1000000
+ * @p - Current loss event rate (0-1) scaled by %TFRC_SCALE
* @s - Packet size in bytes
* @t_rto - Nofeedback Timer setting in usecs
* @t_ipi - Interpacket (send) interval (RFC 3448, 4.6) in usecs
@@ -90,7 +85,6 @@ enum ccid3_hc_tx_states {
* @t_nom - Nominal send time of next packet
* @delta - Send timer delta (RFC 3448, 4.6) in usecs
* @hist - Packet history
- * @options_received - Parsed set of retrieved options
*/
struct ccid3_hc_tx_sock {
u64 x;
@@ -109,7 +103,6 @@ struct ccid3_hc_tx_sock {
ktime_t t_nom;
u32 delta;
struct tfrc_tx_hist_entry *hist;
- struct ccid3_options_received options_received;
};
static inline struct ccid3_hc_tx_sock *ccid3_hc_tx_sk(const struct sock *sk)
--- a/net/dccp/ccids/lib/tfrc.h
+++ b/net/dccp/ccids/lib/tfrc.h
@@ -28,11 +28,20 @@ extern int tfrc_debug;
#define tfrc_pr_debug(format, a...)
#endif
-/* integer-arithmetic divisions of type (a * 1000000)/b */
+/*
+ * Routines and constants to perform scaled fixpoint arithmetic.
+ *
+ * To avoid carrying around the remainder of division operations, we scale all
+ * division operations by %TFRC_SCALE. The current factor is balanced, i.e. will
+ * not produce u32 overflow under reasonable conditions. In places where very
+ * large values could occur, scaled_div32() performs an additional sanity check.
+ */
+#define TFRC_SCALE 1000000
+
static inline u64 scaled_div(u64 a, u32 b)
{
BUG_ON(b==0);
- a *= 1000000;
+ a *= TFRC_SCALE;
do_div(a, b);
return a;
}
@@ -50,6 +59,19 @@ static inline u32 scaled_div32(u64 a, u32 b)
}
/**
+ * tfrc_invert_loss_rate - Invert reciprocal to give scaled Loss Event Rate p
+ * Maps @reciprocal into a percentage p so that 100% corresponds to %TFRC_SCALE.
+ * The highest possible value, 1/0, is mapped into 100%. The smallest possible
+ * value 1/UINT_MAX is rounded down to 0, using the convention of RFC 4342, 8.5.
+ */
+static inline u32 tfrc_invert_loss_rate(const u32 reciprocal)
+{
+ if (reciprocal == UINT_MAX)
+ return 0;
+ return reciprocal <= 1 ? TFRC_SCALE : scaled_div(1, reciprocal);
+}
+
+/**
* tfrc_ewma - Exponentially weighted moving average
* @weight: Weight to be used as damping factor, in units of 1/10
*/
--
1.5.5
The University of Aberdeen is a charity registered in Scotland, No SC013683.
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