Em Fri, Oct 05, 2007 at 11:25:24AM +0100, Gerrit Renker escreveu:
> Arnaldo,
>
> please disregard the earlier suggestion from below regarding ts_recent and feel free
> to do with the structure as you see fit.
>
> To me it seems that the main problems using a RFC1323-like algorithm are
> * the ts_recent field is not enough, the algorithm requires other information (e.g. whether
> an Ack advances the send window) to deal robustly with delays, holes,
> * it is hard to get right (e.g. omments above tcp_ack_saw_tstamp() in tcp_input.c)
> * the current solution of timing both send time and Ack arrival is the simplest
> and has the advantage of being responsive to receiver behaviour (as in CCID3).
> An additional advantage is that the current code already provides Elapsed Time information
> on each Ack Vector, so that dccp_sample_rtt() can be used.
> Maybe CCID2 could benefit by upgrading from jiffies to ktime_t, as this enables to
> better determine whether multiple losses belong to the same RTT (with 1ms resolution
> and Gbps speed this does not work so well).
CCID2 needs a lot of love and care, yes :-\
> Please can you let me know whether:
>
> * the outlined "struct dccp_request_sock" below is still the preferred format;
Please use the outlined one. I haven't checked, but if we use a struct
like in your second option (below) we can end up with struct holes on
64-bit arches.
> * whether as an alternative the dreq_tstamp_{echo,time} fields can be combined, i.e.
> use a fixed member of type
> struct dccp_ts_echo {
> ktime_t ts_time;
> __u32 ts_echo;
> };
> or similar - but without the mallocing, and with overriding each time a new timestamp arrives;
> * or whether a different solution is planned.
>
> I'd need to know so that I can rework the patches and resubmit them accordingly.
>
>
> Quoting Gerrit Renker:
> | Quoting Arnaldo Carvalho de Melo:
> | | I suggest it to become:
> | |
> | | [acme@mica net-2.6.24]$ pahole -C dccp_request_sock net/dccp/minisocks.o
> | |
> | | struct dccp_request_sock {
> | | struct inet_request_sock dreq_inet_rsk; /* 0 56 */
> | | __u64 dreq_iss; /* 56 8 */
> | | /* --- cacheline 1 boundary (64 bytes) --- */
> | | __u64 dreq_isr; /* 64 8 */
> | | __be32 dreq_service; /* 72 4 */
> | | __u32 dreq_tstamp_echo; /* 76 4 */
> | | ktime_t dreq_tstamp_time; /* 80 8 */
> | |
> | | /* size: 88, cachelines: 2 */
> | | /* last cacheline: 24 bytes */
> | | };
> | |
> | | Humm, these minisocks are getting fat... another thing for my TODO list,
> | | request_sock::ts_recent seems to be used only by the TCP machinery, ripe
> | | for the picking....
> |
> | I have thought about this: do you think the following solution is better -
> | the difference between kmallocing and fixed is now between pointer to struct
> | and u64 (ktime_t).
> |
> |
> | struct dccp_request_sock {
> | struct inet_request_sock dreq_inet_rsk;
> | __u64 dreq_iss,
> | dreq_isr;
> | __be32 dreq_service;
> | #define dreq_tstamp_echo dreq_inet_rsk.req.ts_recent
> | ktime_t dreq_tstamp_time;
> | };
> |
> |
> | The only other thing that is required is then to change the insertion routine to
> |
> | dccp_insert_option_timestamp_echo(struct sock *sk, struct dccp_request_sock *dreq,
> | struct sk_buff *skb);
> | /* when @dreq is NULL, @sk is used */
> |
> |
> |
> | On another note I think that the CCID2 code could benefit from using such timestamps also, in particular
> | for high-speed networks.
-
To unsubscribe from this list: send the line "unsubscribe dccp" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
