Re: Overlayfs performance issue

Re: Overlayfs performance issue

[Miklos Szeredi]

On Wed, Jan 20, 2021 at 11:54 PM garyhuang <zjh.20052005@163.com> wrote:
>
> Hi Miklos,
>
> Have you ever come into this?
>
> 1. dockerd with overlay2
>    a. Running nginx in container mounting the host directory which contains the file to be accessed (docker -v xxx:xxx)
>    b. Running nginx in container mounting the host file directly
>    The RPS varies too much (RPS(a) < RPS(b)), the more the workers are, the bigger the discount is
>
> 2. dockerd with devicemapper
>    Running nginx in container with both the same mounting scenarios, the RPS is not discounted
>
> 3. nginx on host, no performance discounted too. The RPS equals to container with devicemapper.
>
> It is kernel related with big extra spinlock consumption observed by perf when running dockerd with overlayfs even the file is mounted from outside host path.

It's not clear where the contention is coming from.  Can you get some
detail from the perf trace where we can see which overlayfs functions
are involved?

Thanks,
Miklos