Date: Wed, 27 Oct 2004 19:18:59 +0400 From: "Andrew P." <infofarmer@mail.ru> To: Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: questions@freebsd.org Subject: Re: Network speed mysteries Message-ID: <417FBC63.8070906@mail.ru> In-Reply-To: <20041027084224.GB72488@happy-idiot-talk.infracaninophile.co.uk> References: <417EA97A.9000206@mail.ru> <20041027084224.GB72488@happy-idiot-talk.infracaninophile.co.uk>
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Matthew Seaman wrote: >On Tue, Oct 26, 2004 at 11:46:02PM +0400, Andrew P. wrote: > > > >>Just an hour ago I decided to rebuild the file-server kernel - and it >>takes time to build it there, as it's an old Celeron box with little >>RAM. By coincidence, some files were being uploaded just when I entered >>"make buildkernel ...". I looked at FileZilla windows, expecting to see >>the speed drop - but WOW! - the speed was at 7Mbytes/s!!! It then >>hovered around 6.5-9Mbytes/s while the kernel was being built! I waited >>for some minutes until the kernel was finally built - and the upload >>speed dropped back to 2.5-3.5Mb/s. I couldn't believe it - and I still >>can't - so I waited and built a kernel once more - with all the same >>effects on speed! It's worth to mention, that when I was installing the >>built kernel, the speed didn't change from usual 3Mb/s. >> >>Please let me know what the heck is going on - or just what you think >>about it. >> >> > >So, when the system is under load, the network throughput goes up? >That must be a timing issue to do with dealing with ACKs -- perhaps >the FreeBSD box just responds too fast for the other end, and loading >down the system delays things just long enough to get both ends into >sync. > >What would be useful would be to use tcpdump(1) or ethereal(1) to >capture a sample of the network traffic in either situation and bring >this up on the freebsd-net@... list. Note that running tcpdump itself >might affect the traffic in a similar way -- there's a thread on >freebsd-net which you might find interesting, starting here: > > http://lists.freebsd.org/pipermail/freebsd-net/2004-October/005368.html > >I you do post to freebsd-net, including the output of 'ifconfig -a' >would be a good move. > > Thanks a lot! When I rebooted after installing my custom kernel, I was delighted to find out that the speed grew to 9.7Mb/s. That's another mystery, cuz I've switched from GENERIC kernel to one with ipfw, ipdivert and some other networking code. So I think I'll just leave it at that. Besides, I don't want to spoil my first impression. I just want to keep wondering - how building a kernel itself can speed up network thruoghput. Real magic :-) Thanks again! Best regards, Andrew P.
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