larger buffer -> slower net transfer?
Don Speck
speck%cit-vlsi at CIT-VAX.ARPA
Sun Oct 6 18:19:39 AEST 1985
The recent comments on ftp speed prompted me to profile
a simple SOCK_STREAM transfer to see if I could make it go
any faster, and I found something very strange: increasing
the write size beyond 1K made the transfer rate *slower*
(in both real and sys time), not faster.
write size sys time (10240K transferred, total)
1K 107 sec
2K 109 sec
1.25K 161 sec
5K 140 sec
10K 123 sec
This must be symptomatic of some great inefficiency in the
4.2bsd kernel. (It happens on both Vax and Sun). Why does
the kernel take longer to split a large write into packets
than if I split it myself? Isn't the rationale for having
it in the kernel "to make it fast"?
Don Speck speck at cit-vax.arpa
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