Unfortunately, the only machine I have access to with an HDD as the
system drive is running Ubuntu 20.04 LTS, which doesn’t have a
multi-threaded version of fixfiles. So I can’t test this on an HDD-only
system.
Still, here are the timings on a 4-core Atom machine with a SATA SSD and
a large SATA HDD data drive mounted at /srv:
$ sudo bash -c 'sync; for i in $(seq 1 3); do echo $i >
/proc/sys/vm/drop_caches; done; time fixfiles -T 1 restore'
[…]
real 6m39.521s
user 5m6.599s
sys 0m42.000s
$ sudo bash -c 'sync; for i in $(seq 1 3); do echo $i >
/proc/sys/vm/drop_caches; done; time fixfiles -T 0 restore'
[…]
real 3m16.602s
user 5m25.444s
sys 0m50.843s
I took care to drop various kernel caches, especially including dentry
and inode caches, to make this more reproducible.
Here are the timings on a very modern 16-core machine with NVMe SSD storage:
$ sudo bash -c 'sync; for i in $(seq 1 3); do echo $i >
/proc/sys/vm/drop_caches; done; time fixfiles -T 1 restore'
[…]
real 3m17.277s
user 2m42.447s
sys 0m24.403s
$ sudo bash -c 'sync; for i in $(seq 1 3); do echo $i >
/proc/sys/vm/drop_caches; done; time fixfiles -T 0 restore'
[…]
real 0m58.154s
user 4m27.209s
sys 0m58.127s
On 7/18/22 11:48, Gary Buhrmaster wrote:
On Mon, Jul 18, 2022 at 6:44 AM Petr Lautrbach<plaut...@redhat.com> wrote:
Dan Čermák<dan.cer...@cgc-instruments.de> writes:
Just out of curiosity, how large is the speedup typically?
It depends on the number of threads your machine has. But you could get some
data for comparison using `fixfiles -T 1 restore` and `fixfiles -T 0
restore` on a running system. The following times are reported on my
workstation:
Has anyone run such a test on a system using
classic ("spinning rust") HDDs? It is sometimes
the case that parallelizing activities that are I/O
intensive can result in excessive seek activity
that can result in rather elongated elapsed times
(much worse than single threaded operation).
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