[Libguestfs] [PATCH libnbd 3/3] examples: copy-libev.c: Support extents

[Nir Soffer]

On Mon, Mar 8, 2021 at 11:50 AM Richard W.M. Jones <rjones at redhat.com>
wrote:

> On Mon, Mar 08, 2021 at 01:26:44AM +0200, Nir Soffer wrote:
> > $ strace -f -c ../copy/nbdcopy --sparse=1048576 --request-size=1048576
> > --requests=16 --connections=1 $SRC $DST
> > strace: Process 1094611 attached
> > strace: Process 1094612 attached
> > strace: Process 1094613 attached
> > strace: Process 1094614 attached
> > strace: Process 1094615 attached
> > strace: Process 1094616 attached
> > strace: Process 1094617 attached
> > strace: Process 1094618 attached
> > strace: Process 1094619 attached
> > strace: Process 1094620 attached
> > strace: Process 1094621 attached
> > strace: Process 1094622 attached
> > strace: Process 1094623 attached
> > strace: Process 1094641 attached
> >
> > (Not sure why we start so many threads with --connections=1 - bug?)
>
> I'm not sure of the exact command, so I used:
>
>   $ ./run nbdcopy --sparse=1048576 --request-size=1048576 --requests=16
> --connections=1 -- [ qemu-nbd -f qcow2 -t ~/fedora-32.qcow2 ] [ nbdkit
> memory 6G ]
>
> Temporarily adding -v shows:
>
>   nbdcopy: src: nbd_ops "qemu-nbd"
>   nbdcopy: src: size=6442450944
>   nbdcopy: dst: nbd_ops "nbdkit"
>   nbdcopy: dst: size=6442450944
>   nbdcopy: connections=1 requests=16 threads=1 synchronous=false
>                                      ^^^^^^^^^
>
> Many threads were created but they all appeared to be associated with
> the ./run script, qemu-nbd and nbdkit.  nbdcopy should only create one
> worker thread in this scenario.
>

Right, I was testing the run script instead of .libs/xxx. When running the
actual executable we see:

$ strace -f -c ../copy/.libs/nbdcopy --flush --sparse=1048576
--request-size=1048576 --requests=16 --connections=1 $SRC $DST
strace: Process 1142801 attached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 59.70    0.914059      914059         1           futex
 18.90    0.289297          17     16768         1 recvfrom
 17.99    0.275497          32      8380         4 sendto
  2.73    0.041852           4      8921           poll
  0.50    0.007616         230        33           madvise
...

$ strace -c .libs/copy-libev $SRC $DST
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 50.25    0.297711          19     15446         1 recvfrom
 39.81    0.235824          34      6863           sendto
  7.69    0.045573           5      8911           epoll_wait
  1.04    0.006132           4      1317           epoll_ctl
  0.42    0.002478          24       103           mmap
 ...

Why do we use the run script?
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