* [PATCH] tcp: bug fix in proportional rate reduction.
@ 2013-05-21 0:22 Nandita Dukkipati
2013-05-21 1:46 ` Neal Cardwell
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Nandita Dukkipati @ 2013-05-21 0:22 UTC (permalink / raw)
To: David S. Miller
Cc: netdev, Eric Dumazet, Neal Cardwell, Yuchung Cheng, Nandita Dukkipati
This patch is a fix for a bug triggering newly_acked_sacked < 0
in tcp_ack(.).
The bug is triggered by sacked_out decreasing relative to prior_sacked,
but packets_out remaining the same as pior_packets. This is because the
snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
prior_sacked is captured before tcp_sacktag_write_queue(). The problem
is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
adjusts the pcount for packets_out and sacked_out (MSS change or other
reason). As a result, this delta in pcount is reflected in
(prior_sacked - sacked_out) but not in (prior_packets - packets_out).
This patch does the following:
1) initializes prior_packets at the start of tcp_ack() so as to
capture the delta in packets_out created by tcp_fragment.
2) introduces a new "previous_packets_out" variable that snapshots
packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
correctly computed as before.
Signed-off-by: Nandita Dukkipati <nanditad@google.com>
---
net/ipv4/tcp_input.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d7d3694..2986e10 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3265,9 +3265,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
bool is_dupack = false;
u32 prior_in_flight;
u32 prior_fackets;
- int prior_packets;
+ int prior_packets = tp->packets_out;
int prior_sacked = tp->sacked_out;
int pkts_acked = 0;
+ int previous_packets_out = 0;
/* If the ack is older than previous acks
* then we can probably ignore it.
@@ -3338,14 +3339,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
sk->sk_err_soft = 0;
icsk->icsk_probes_out = 0;
tp->rcv_tstamp = tcp_time_stamp;
- prior_packets = tp->packets_out;
if (!prior_packets)
goto no_queue;
/* See if we can take anything off of the retransmit queue. */
+ previous_packets_out = tp->packets_out;
flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
- pkts_acked = prior_packets - tp->packets_out;
+ pkts_acked = previous_packets_out - tp->packets_out;
if (tcp_ack_is_dubious(sk, flag)) {
/* Advance CWND, if state allows this. */
--
1.8.2.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] tcp: bug fix in proportional rate reduction.
2013-05-21 0:22 [PATCH] tcp: bug fix in proportional rate reduction Nandita Dukkipati
@ 2013-05-21 1:46 ` Neal Cardwell
2013-05-21 15:18 ` Yuchung Cheng
2013-05-22 1:12 ` [PATCH v2] " Nandita Dukkipati
2 siblings, 0 replies; 7+ messages in thread
From: Neal Cardwell @ 2013-05-21 1:46 UTC (permalink / raw)
To: Nandita Dukkipati; +Cc: David S. Miller, Netdev, Eric Dumazet, Yuchung Cheng
On Mon, May 20, 2013 at 8:22 PM, Nandita Dukkipati <nanditad@google.com> wrote:
> This patch is a fix for a bug triggering newly_acked_sacked < 0
> in tcp_ack(.).
>
> The bug is triggered by sacked_out decreasing relative to prior_sacked,
> but packets_out remaining the same as pior_packets. This is because the
> snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
> prior_sacked is captured before tcp_sacktag_write_queue(). The problem
> is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
> adjusts the pcount for packets_out and sacked_out (MSS change or other
> reason). As a result, this delta in pcount is reflected in
> (prior_sacked - sacked_out) but not in (prior_packets - packets_out).
>
> This patch does the following:
> 1) initializes prior_packets at the start of tcp_ack() so as to
> capture the delta in packets_out created by tcp_fragment.
> 2) introduces a new "previous_packets_out" variable that snapshots
> packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
> correctly computed as before.
>
> Signed-off-by: Nandita Dukkipati <nanditad@google.com>
> ---
> net/ipv4/tcp_input.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
Acked-by: Neal Cardwell <ncardwell@google.com>
neal
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] tcp: bug fix in proportional rate reduction.
2013-05-21 0:22 [PATCH] tcp: bug fix in proportional rate reduction Nandita Dukkipati
2013-05-21 1:46 ` Neal Cardwell
@ 2013-05-21 15:18 ` Yuchung Cheng
2013-05-22 1:12 ` Nandita Dukkipati
2013-05-22 1:12 ` [PATCH v2] " Nandita Dukkipati
2 siblings, 1 reply; 7+ messages in thread
From: Yuchung Cheng @ 2013-05-21 15:18 UTC (permalink / raw)
To: Nandita Dukkipati; +Cc: David S. Miller, netdev, Eric Dumazet, Neal Cardwell
On Mon, May 20, 2013 at 5:22 PM, Nandita Dukkipati <nanditad@google.com> wrote:
> This patch is a fix for a bug triggering newly_acked_sacked < 0
> in tcp_ack(.).
>
> The bug is triggered by sacked_out decreasing relative to prior_sacked,
> but packets_out remaining the same as pior_packets. This is because the
> snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
> prior_sacked is captured before tcp_sacktag_write_queue(). The problem
> is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
> adjusts the pcount for packets_out and sacked_out (MSS change or other
> reason). As a result, this delta in pcount is reflected in
> (prior_sacked - sacked_out) but not in (prior_packets - packets_out).
I don't think this patch fixes the problem you described because
it does not change how newly_acked_sacked is computed.
you probably should use prior_packets for newly_acked_sacked and use
previous_packets_out for pkts_acked
>
> This patch does the following:
> 1) initializes prior_packets at the start of tcp_ack() so as to
> capture the delta in packets_out created by tcp_fragment.
> 2) introduces a new "previous_packets_out" variable that snapshots
> packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
> correctly computed as before.
>
> Signed-off-by: Nandita Dukkipati <nanditad@google.com>
> ---
> net/ipv4/tcp_input.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index d7d3694..2986e10 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3265,9 +3265,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> bool is_dupack = false;
> u32 prior_in_flight;
> u32 prior_fackets;
> - int prior_packets;
> + int prior_packets = tp->packets_out;
> int prior_sacked = tp->sacked_out;
> int pkts_acked = 0;
> + int previous_packets_out = 0;
>
> /* If the ack is older than previous acks
> * then we can probably ignore it.
> @@ -3338,14 +3339,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> sk->sk_err_soft = 0;
> icsk->icsk_probes_out = 0;
> tp->rcv_tstamp = tcp_time_stamp;
> - prior_packets = tp->packets_out;
> if (!prior_packets)
> goto no_queue;
>
> /* See if we can take anything off of the retransmit queue. */
> + previous_packets_out = tp->packets_out;
> flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
>
> - pkts_acked = prior_packets - tp->packets_out;
> + pkts_acked = previous_packets_out - tp->packets_out;
>
> if (tcp_ack_is_dubious(sk, flag)) {
> /* Advance CWND, if state allows this. */
> --
> 1.8.2.1
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v2] tcp: bug fix in proportional rate reduction.
2013-05-21 0:22 [PATCH] tcp: bug fix in proportional rate reduction Nandita Dukkipati
2013-05-21 1:46 ` Neal Cardwell
2013-05-21 15:18 ` Yuchung Cheng
@ 2013-05-22 1:12 ` Nandita Dukkipati
2013-05-22 1:27 ` Yuchung Cheng
2 siblings, 1 reply; 7+ messages in thread
From: Nandita Dukkipati @ 2013-05-22 1:12 UTC (permalink / raw)
To: David S. Miller
Cc: netdev, Eric Dumazet, Neal Cardwell, Yuchung Cheng, Nandita Dukkipati
This patch is a fix for a bug triggering newly_acked_sacked < 0
in tcp_ack(.).
The bug is triggered by sacked_out decreasing relative to prior_sacked,
but packets_out remaining the same as pior_packets. This is because the
snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
prior_sacked is captured before tcp_sacktag_write_queue(). The problem
is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
adjusts the pcount for packets_out and sacked_out (MSS change or other
reason). As a result, this delta in pcount is reflected in
(prior_sacked - sacked_out) but not in (prior_packets - packets_out).
This patch does the following:
1) initializes prior_packets at the start of tcp_ack() so as to
capture the delta in packets_out created by tcp_fragment.
2) introduces a new "previous_packets_out" variable that snapshots
packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
correctly computed as before.
3) Computes pkts_acked using previous_packets_out, and computes
newly_acked_sacked using prior_packets.
Signed-off-by: Nandita Dukkipati <nanditad@google.com>
---
Changelog since v1:
- Compute newly_acked_sacked using prior_packets.
net/ipv4/tcp_input.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d7d3694..8230cd6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2679,8 +2679,8 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
* tcp_xmit_retransmit_queue().
*/
static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
- int prior_sacked, bool is_dupack,
- int flag)
+ int prior_sacked, int prior_packets,
+ bool is_dupack, int flag)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
@@ -2740,7 +2740,8 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
tcp_add_reno_sack(sk);
} else
do_lost = tcp_try_undo_partial(sk, pkts_acked);
- newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
+ newly_acked_sacked = prior_packets - tp->packets_out +
+ tp->sacked_out - prior_sacked;
break;
case TCP_CA_Loss:
tcp_process_loss(sk, flag, is_dupack);
@@ -2754,7 +2755,8 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
if (is_dupack)
tcp_add_reno_sack(sk);
}
- newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
+ newly_acked_sacked = prior_packets - tp->packets_out +
+ tp->sacked_out - prior_sacked;
if (icsk->icsk_ca_state <= TCP_CA_Disorder)
tcp_try_undo_dsack(sk);
@@ -3265,9 +3267,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
bool is_dupack = false;
u32 prior_in_flight;
u32 prior_fackets;
- int prior_packets;
+ int prior_packets = tp->packets_out;
int prior_sacked = tp->sacked_out;
int pkts_acked = 0;
+ int previous_packets_out = 0;
/* If the ack is older than previous acks
* then we can probably ignore it.
@@ -3338,14 +3341,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
sk->sk_err_soft = 0;
icsk->icsk_probes_out = 0;
tp->rcv_tstamp = tcp_time_stamp;
- prior_packets = tp->packets_out;
if (!prior_packets)
goto no_queue;
/* See if we can take anything off of the retransmit queue. */
+ previous_packets_out = tp->packets_out;
flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
- pkts_acked = prior_packets - tp->packets_out;
+ pkts_acked = previous_packets_out - tp->packets_out;
if (tcp_ack_is_dubious(sk, flag)) {
/* Advance CWND, if state allows this. */
@@ -3353,7 +3356,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
tcp_cong_avoid(sk, ack, prior_in_flight);
is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
- is_dupack, flag);
+ prior_packets, is_dupack, flag);
} else {
if (flag & FLAG_DATA_ACKED)
tcp_cong_avoid(sk, ack, prior_in_flight);
@@ -3376,7 +3379,7 @@ no_queue:
/* If data was DSACKed, see if we can undo a cwnd reduction. */
if (flag & FLAG_DSACKING_ACK)
tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
- is_dupack, flag);
+ prior_packets, is_dupack, flag);
/* If this ack opens up a zero window, clear backoff. It was
* being used to time the probes, and is probably far higher than
* it needs to be for normal retransmission.
@@ -3399,7 +3402,7 @@ old_ack:
if (TCP_SKB_CB(skb)->sacked) {
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
- is_dupack, flag);
+ prior_packets, is_dupack, flag);
}
SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
--
1.8.2.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] tcp: bug fix in proportional rate reduction.
2013-05-21 15:18 ` Yuchung Cheng
@ 2013-05-22 1:12 ` Nandita Dukkipati
0 siblings, 0 replies; 7+ messages in thread
From: Nandita Dukkipati @ 2013-05-22 1:12 UTC (permalink / raw)
To: Yuchung Cheng; +Cc: David S. Miller, netdev, Eric Dumazet, Neal Cardwell
On Tue, May 21, 2013 at 8:18 AM, Yuchung Cheng <ycheng@google.com> wrote:
> On Mon, May 20, 2013 at 5:22 PM, Nandita Dukkipati <nanditad@google.com> wrote:
>> This patch is a fix for a bug triggering newly_acked_sacked < 0
>> in tcp_ack(.).
>>
>> The bug is triggered by sacked_out decreasing relative to prior_sacked,
>> but packets_out remaining the same as pior_packets. This is because the
>> snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
>> prior_sacked is captured before tcp_sacktag_write_queue(). The problem
>> is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
>> adjusts the pcount for packets_out and sacked_out (MSS change or other
>> reason). As a result, this delta in pcount is reflected in
>> (prior_sacked - sacked_out) but not in (prior_packets - packets_out).
> I don't think this patch fixes the problem you described because
> it does not change how newly_acked_sacked is computed.
>
> you probably should use prior_packets for newly_acked_sacked and use
> previous_packets_out for pkts_acked
Good catch, you are absolutely right. Sent a v2.
>
>>
>> This patch does the following:
>> 1) initializes prior_packets at the start of tcp_ack() so as to
>> capture the delta in packets_out created by tcp_fragment.
>> 2) introduces a new "previous_packets_out" variable that snapshots
>> packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
>> correctly computed as before.
>>
>> Signed-off-by: Nandita Dukkipati <nanditad@google.com>
>> ---
>> net/ipv4/tcp_input.c | 7 ++++---
>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index d7d3694..2986e10 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -3265,9 +3265,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
>> bool is_dupack = false;
>> u32 prior_in_flight;
>> u32 prior_fackets;
>> - int prior_packets;
>> + int prior_packets = tp->packets_out;
>> int prior_sacked = tp->sacked_out;
>> int pkts_acked = 0;
>> + int previous_packets_out = 0;
>>
>> /* If the ack is older than previous acks
>> * then we can probably ignore it.
>> @@ -3338,14 +3339,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
>> sk->sk_err_soft = 0;
>> icsk->icsk_probes_out = 0;
>> tp->rcv_tstamp = tcp_time_stamp;
>> - prior_packets = tp->packets_out;
>> if (!prior_packets)
>> goto no_queue;
>>
>> /* See if we can take anything off of the retransmit queue. */
>> + previous_packets_out = tp->packets_out;
>> flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
>>
>> - pkts_acked = prior_packets - tp->packets_out;
>> + pkts_acked = previous_packets_out - tp->packets_out;
>>
>> if (tcp_ack_is_dubious(sk, flag)) {
>> /* Advance CWND, if state allows this. */
>> --
>> 1.8.2.1
>>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] tcp: bug fix in proportional rate reduction.
2013-05-22 1:12 ` [PATCH v2] " Nandita Dukkipati
@ 2013-05-22 1:27 ` Yuchung Cheng
2013-05-23 7:10 ` David Miller
0 siblings, 1 reply; 7+ messages in thread
From: Yuchung Cheng @ 2013-05-22 1:27 UTC (permalink / raw)
To: Nandita Dukkipati; +Cc: David S. Miller, netdev, Eric Dumazet, Neal Cardwell
On Tue, May 21, 2013 at 6:12 PM, Nandita Dukkipati <nanditad@google.com> wrote:
> This patch is a fix for a bug triggering newly_acked_sacked < 0
> in tcp_ack(.).
>
> The bug is triggered by sacked_out decreasing relative to prior_sacked,
> but packets_out remaining the same as pior_packets. This is because the
> snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
> prior_sacked is captured before tcp_sacktag_write_queue(). The problem
> is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
> adjusts the pcount for packets_out and sacked_out (MSS change or other
> reason). As a result, this delta in pcount is reflected in
> (prior_sacked - sacked_out) but not in (prior_packets - packets_out).
>
> This patch does the following:
> 1) initializes prior_packets at the start of tcp_ack() so as to
> capture the delta in packets_out created by tcp_fragment.
> 2) introduces a new "previous_packets_out" variable that snapshots
> packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
> correctly computed as before.
> 3) Computes pkts_acked using previous_packets_out, and computes
> newly_acked_sacked using prior_packets.
>
> Signed-off-by: Nandita Dukkipati <nanditad@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
> ---
> Changelog since v1:
> - Compute newly_acked_sacked using prior_packets.
>
> net/ipv4/tcp_input.c | 23 +++++++++++++----------
> 1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index d7d3694..8230cd6 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -2679,8 +2679,8 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
> * tcp_xmit_retransmit_queue().
> */
> static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
> - int prior_sacked, bool is_dupack,
> - int flag)
> + int prior_sacked, int prior_packets,
> + bool is_dupack, int flag)
> {
> struct inet_connection_sock *icsk = inet_csk(sk);
> struct tcp_sock *tp = tcp_sk(sk);
> @@ -2740,7 +2740,8 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
> tcp_add_reno_sack(sk);
> } else
> do_lost = tcp_try_undo_partial(sk, pkts_acked);
> - newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
> + newly_acked_sacked = prior_packets - tp->packets_out +
> + tp->sacked_out - prior_sacked;
> break;
> case TCP_CA_Loss:
> tcp_process_loss(sk, flag, is_dupack);
> @@ -2754,7 +2755,8 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
> if (is_dupack)
> tcp_add_reno_sack(sk);
> }
> - newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
> + newly_acked_sacked = prior_packets - tp->packets_out +
> + tp->sacked_out - prior_sacked;
>
> if (icsk->icsk_ca_state <= TCP_CA_Disorder)
> tcp_try_undo_dsack(sk);
> @@ -3265,9 +3267,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> bool is_dupack = false;
> u32 prior_in_flight;
> u32 prior_fackets;
> - int prior_packets;
> + int prior_packets = tp->packets_out;
> int prior_sacked = tp->sacked_out;
> int pkts_acked = 0;
> + int previous_packets_out = 0;
>
> /* If the ack is older than previous acks
> * then we can probably ignore it.
> @@ -3338,14 +3341,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> sk->sk_err_soft = 0;
> icsk->icsk_probes_out = 0;
> tp->rcv_tstamp = tcp_time_stamp;
> - prior_packets = tp->packets_out;
> if (!prior_packets)
> goto no_queue;
>
> /* See if we can take anything off of the retransmit queue. */
> + previous_packets_out = tp->packets_out;
> flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
>
> - pkts_acked = prior_packets - tp->packets_out;
> + pkts_acked = previous_packets_out - tp->packets_out;
>
> if (tcp_ack_is_dubious(sk, flag)) {
> /* Advance CWND, if state allows this. */
> @@ -3353,7 +3356,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> tcp_cong_avoid(sk, ack, prior_in_flight);
> is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
> tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
> - is_dupack, flag);
> + prior_packets, is_dupack, flag);
> } else {
> if (flag & FLAG_DATA_ACKED)
> tcp_cong_avoid(sk, ack, prior_in_flight);
> @@ -3376,7 +3379,7 @@ no_queue:
> /* If data was DSACKed, see if we can undo a cwnd reduction. */
> if (flag & FLAG_DSACKING_ACK)
> tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
> - is_dupack, flag);
> + prior_packets, is_dupack, flag);
> /* If this ack opens up a zero window, clear backoff. It was
> * being used to time the probes, and is probably far higher than
> * it needs to be for normal retransmission.
> @@ -3399,7 +3402,7 @@ old_ack:
> if (TCP_SKB_CB(skb)->sacked) {
> flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
> tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
> - is_dupack, flag);
> + prior_packets, is_dupack, flag);
> }
>
> SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
> --
> 1.8.2.1
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] tcp: bug fix in proportional rate reduction.
2013-05-22 1:27 ` Yuchung Cheng
@ 2013-05-23 7:10 ` David Miller
0 siblings, 0 replies; 7+ messages in thread
From: David Miller @ 2013-05-23 7:10 UTC (permalink / raw)
To: ycheng; +Cc: nanditad, netdev, edumazet, ncardwell
From: Yuchung Cheng <ycheng@google.com>
Date: Tue, 21 May 2013 18:27:09 -0700
> On Tue, May 21, 2013 at 6:12 PM, Nandita Dukkipati <nanditad@google.com> wrote:
>> This patch is a fix for a bug triggering newly_acked_sacked < 0
>> in tcp_ack(.).
>>
>> The bug is triggered by sacked_out decreasing relative to prior_sacked,
>> but packets_out remaining the same as pior_packets. This is because the
>> snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
>> prior_sacked is captured before tcp_sacktag_write_queue(). The problem
>> is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
>> adjusts the pcount for packets_out and sacked_out (MSS change or other
>> reason). As a result, this delta in pcount is reflected in
>> (prior_sacked - sacked_out) but not in (prior_packets - packets_out).
>>
>> This patch does the following:
>> 1) initializes prior_packets at the start of tcp_ack() so as to
>> capture the delta in packets_out created by tcp_fragment.
>> 2) introduces a new "previous_packets_out" variable that snapshots
>> packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
>> correctly computed as before.
>> 3) Computes pkts_acked using previous_packets_out, and computes
>> newly_acked_sacked using prior_packets.
>>
>> Signed-off-by: Nandita Dukkipati <nanditad@google.com>
> Acked-by: Yuchung Cheng <ycheng@google.com>
Applied, and queued up for -stable, thanks.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2013-05-23 7:10 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-05-21 0:22 [PATCH] tcp: bug fix in proportional rate reduction Nandita Dukkipati
2013-05-21 1:46 ` Neal Cardwell
2013-05-21 15:18 ` Yuchung Cheng
2013-05-22 1:12 ` Nandita Dukkipati
2013-05-22 1:12 ` [PATCH v2] " Nandita Dukkipati
2013-05-22 1:27 ` Yuchung Cheng
2013-05-23 7:10 ` David Miller
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