Re: [Libguestfs] [PATCH libnbd 3/3] examples: copy-libev.c: Support extents
On 3/7/21 5:26 PM, Nir Soffer wrote:
On Mon, Mar 8, 2021 at 12:59 AM Nir Soffer <nsoffer(a)redhat.com>
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?)
Known issue in nbdkit. Right now, nbdkit defaults a parallel plugin to
16 threads (altered when using a plugin that has a serialized thread
model, or if you use the command-line option --threads=1), and starts
all of those threads regardless of how many parallel requests the client
actually sends. One of the TODO items is to refactor it to have nbdkit
use a thread pool, which starts with just one worker thread, and can add
workers up to the --threads limit, but where workers are added only when
under actual pressure from parallel guest commands.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org