On 11/06/15 21:46, Cui, Cheng wrote:
Hello Hans,
Sorry if my previous email does not reach you because of a bad subject.
This is Cheng Cui. I am reading the CURRENT FreeBSD code in tcp_output.c, and
find this question regarding your change in revision 271946.
https://svnweb.freebsd.org/base/head/sys/netinet/tcp_output.c?r1=271946&r2=271945&pathrev=271946
trim data "len" under TSO:
885 /*
886 * Prevent the last segment from being
887 * fractional unless the send sockbuf can be
888 * emptied:
889 */
890 max_len = (tp->t_maxopd - optlen);
891 if ((off + len) < sbavail(&so->so_snd)) { <==
892 moff = len % max_len;
893 if (moff != 0) {
894 len -= moff;
895 sendalot = 1;
896 }
897 }
Is there a specific reason that it should skip trimming the data "len" under the condition of
"(off + len) == sbavail(&so->so_snd)" in TSO?
> Because I am wondering if we can trim the data "len" directly without
checking the "(off + len)" condition.
Hi Cheng,
I believe the reason is to avoid looping one more time outputting a
single packet containing the remainder of the available data, with
regard to max_len. How did you envision the removal of this check would
influence the generated packet sequence?
--HPS
Thanks,
--Cheng Cui
NetApp Scale Out Networking
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