So in practice it was reading several KiB at a time, doing zero-copy.

> Also, the fact that my throughput is so much higher than yours (on a
> several-year-old computer) is interesting.  Obviously I have a faster
> net connection (wget reports 1.19M/s),

So for you wget is ~2.5 times faster than Guile, right?

[...]

>> Looking at the strace output reveals no real difference: they all make
>> one syscall for each chunk of 1410 bytes.
>>
>> ‘time’ reports that Guile spends 0.2 s. in user and 0.8 s. in system,
>> both of which are an order of magnitude higher than wget/curl.
>
> If they make essentially the same syscalls, then why would the system
> time be an order of magnitude higher?  Something doesn't sound right
> here.

I concur.

I’ve tried Linux perf and OProfile but failed to get useful info.

Ludo’.