Date: Thu, 29 May 2003 09:20:50 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Terry Lambert <tlambert2@mindspring.com> Cc: arch@freebsd.org Subject: Re: sendfile(2) SF_NOPUSH flag proposal Message-ID: <200305291620.h4TGKobi078312@apollo.backplane.com> References: <200305281755.h4SHtbu05504@windsor.research.att.com> <3ED5961E.5DE0F41B@mindspring.com>
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:Bill Fenner wrote:
:> Why not set PRUS_MORETOCOME on all but the final pru_send() call?
:
:If the file is larger than `sysctl net.inet.tcp.sendspace`, then
:this code in do_sendfile():
:
: if (sbspace(&so->so_snd) < so->so_snd.sb_lowat) {
: if (so->so_state & SS_NBIO) {
: m_freem(m);
: sbunlock(&so->so_snd);
: splx(s);
: error = EAGAIN;
: goto done;
: }
: error = sbwait(&so->so_snd);
:
:will result in you sleeping with PRUS_MORETOCOME set, but with
:no more being sent because the send buffer doesn't get emptied,
:as it's waiting for more data to send.
:
:-- Terry
Not unless the send buffer is substantially near the size of a single
packet, which it isn't (it's far larger). PRUS_MORETOCOME is smarter
then that, Terry. tcp_output() just uses it as a hint, it doesn't
unconditionally hold off a flush.
The code to refer to is netinet/tcp_output.c around line 313 (in stable),
in tcp_output(). The section within the if (len) { ... } sequence.
This section does all tests related to sending a packet and as you can
see TF_MORETOCOME will not prevent the data from being flushed the
more there is enough to fill a packet.
-Matt
Matthew Dillon
<dillon@backplane.com>
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