Messages in this thread | | | Date | Sat, 1 Jan 2000 01:38:17 +0000 | From | Pavel Machek <> | Subject | Re: Linux 2.4.1 network (socket) performance |
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Hi!
> Hello, I am trying to find the reason for very, very poor network > performance with sustained data transfers on Linux 2.4.1. I found > a work-around, but don't think user-mode code should have to provide > such work-arounds. > > In the following, with Linux 2.4.1, on a dedicated 100/Base > link: > > s = socket connected to DISCARD (null-sink) server. > > while(len) > { > stat = write(s, buf, min(len, MTU)); > /* Yes, I do check for an error */ > buf += stat; > len -= stat; > } > > Data length is 0x00010000 bytes. > > MTU Average trans rate Fastest trans rate > ---- ----------------- ----------------- > 65536 0.468 Mb/s 0.902 Mb/s > 32768 0.684 Mb/s 0.813 Mb/s > 16384 2.989 Mb/s 3.121 Mb/s > 8192 5.211 Mb/s 6.160 Mb/s > 4094 8.212 Mb/s 9.101 Mb/s > 2048 8.561 Mb/s 9.280 Mb/s > 1024 7.250 Mb/s 7.500 Mb/s > 512 4.818 Mb/s 5.107 Mb/s > > As you can see, there is a maximum data length that can be > handled with reasonable speed from a socket. Trying to find > out what that was, I discovered that the best MTU was 3924. > I don't know why. It shows:
Looks like that's page_size - epsilon.
> MTU Average trans rate Fastest trans rate > ---- ----------------- ----------------- > 3924 8.920 Mb/s 9.31 Mb/s
But even this is *not* reasonable speed for 100MBit ethernet!
> If the user's data length is higher than this, there is a 1/100th > of a second wait between packets. The larger the user's data length, > the more the data gets chopped up into 1/100th of a second intervals. > > It looks as though user data that can't fit into two Ethernet packets > is queued until the next time-slice on a 100 Hz system. This severely > hurts sustained data performance. The performance with a single > 64k data buffer is abysmal. If it gets chopped up into 2048 byte > blocks in user-space, it's reasonable. > > Both machines are Dual Pentium 600 MHz machines with identical eepro100 > Ethernet boards. I substituted, LANCE (Hewlett Packard), and 3COM boards > (3c59x) with essentially no change.
Strange. Do you have interrupts working okay? [I'm able to get 4Mbit with ne2000 hooked on timer IRQ, so this is not totally stupid Question.]
> Does this point out a problem? Or should user-mode code be required
Definitely problem.
> to chop up data lengths to something more "reasonable" for the kernel? > If so, how does the user know what "reasonable" is?
-- Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt, details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.
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