Date: Tue, 27 May 2003 16:03:04 +0400 (MSD) From: Igor Sysoev <is@rambler-co.ru> To: Peter Jeremy <peterjeremy@optushome.com.au> Cc: arch@freebsd.org Subject: Re: sendfile(2) SF_NOPUSH flag proposal Message-ID: <Pine.BSF.4.21.0305271533060.46491-100000@is> In-Reply-To: <20030527113138.GD44520@cirb503493.alcatel.com.au>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, 27 May 2003, Peter Jeremy wrote: > On Tue, May 27, 2003 at 02:49:35PM +0400, Igor Sysoev wrote: > >Actually 6 vs. 6 for this 8K file. But I said about another thing. > >Let's see 48K file and 250 bytes header. sendfile() usually sends > >it as 4K or 8K hunks so there are 48/8 * 6 + 1 (header) = 37 packets. > >But (48K + 250) / 1460 = 33 * 1460 + 1270 i.e. 34 packets. > >It's 8% decrease of data packets. Add here the possible retransmitions. > > Why is the number of data packets so important? If you repeat the > calculation considering bytes across the wire (assuming Ethernet), > then the saving is closer to 0.4% - this is in the noise. When there's the simple way to avoid the partially filled packets I do not see any reason not to use it. > For that matter, have you considered the impact of Path MTU discovery? What impact ? > I think possible retransmissions are irrelevant here. If your packet > loss is anything above negligible then you have other problems. If > the retransmission is caused by transmission noise, then the smaller > packets are less likely to get hit. And the sender is likely to > retransmit a full packet rather than the small packet originally sent. > > >> Really: it's in the noise. Unless you are paying by packet > >> count, you probably shouldn't care. > > > >So do you consider that IP fragmentation is the good thing ? > > "IP fragmentation" normally refers to a single IP packet being > split up into multiple smaller packets by a router. It has nothing > to do with the topic under discussion. If anything, transmitting I know what is IP fragmentation. But in terms of the packet overhead they are similar to not full packets. > smaller IP packets reduces the likelihood that an intervening router > will need to fragment packets - so your patch actually increases > the probability of IP fragmentation. Yes, I understand it. Igor Sysoev http://sysoev.ru/en/
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.4.21.0305271533060.46491-100000>