Re: [PATCH 8/8] nfsd: default to a more sane number of threads

[Chuck Lever <chuck.lever@oracle.com>]

On Wed, Mar 20, 2024 at 09:11:31AM -0400, Jeff Layton wrote:
> Add a small script that can estimate the number of threads for
> nfsd. We default to 32 threads for every GB of guest memory.
> 
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  kconfigs/Kconfig.nfsd      |  2 +-
>  scripts/nfsd-thread-est.sh | 15 +++++++++++++++
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/kconfigs/Kconfig.nfsd b/kconfigs/Kconfig.nfsd
> index dec98c1e964f..7c28ad98955a 100644
> --- a/kconfigs/Kconfig.nfsd
> +++ b/kconfigs/Kconfig.nfsd
> @@ -69,7 +69,7 @@ config NFSD_EXPORT_OPTIONS
>  
>  config NFSD_THREADS
>  	int "Number of nfsd threads to spawn"
> -	default 8
> +	default $(shell, scripts/nfsd-thread-est.sh)
>  	help
>  	  Number of nfsd threads to start up for testing.
>  
> diff --git a/scripts/nfsd-thread-est.sh b/scripts/nfsd-thread-est.sh
> new file mode 100755
> index 000000000000..dc5a1deb1215
> --- /dev/null
> +++ b/scripts/nfsd-thread-est.sh
> @@ -0,0 +1,15 @@
> +#!/bin/bash
> +#
> +# The default number of 8 nfsd threads is pitifully low!
> +#
> +#
> +# Each nfsd thread consumes ~1MB of memory, long-term:
> +#
> +# stack, kthread overhead, svc_rqst, and the rq_pages array, plus
> +# temporary working space.
> +#
> +# Allow 32 threads for each GB of guest memory:

I agree that 8 is a small number, but that multiplier seems
excessive. On my 16GB test systems, that would create 512 threads.
I set the nfsd thread count to 32 on my test NFS server, and I've
never seen more than 10-15 threads for any test. (OK, maybe I should
run tests that drive the test server harder).

Plus, no distribution uses that configuration. Maybe we should stick
to what's a common deployment scenario?

Do you have data that shows creating more threads improves test run
time?


> +
> +. "${TOPDIR}/.config"
> +
> +echo "$(( 32 * $CONFIG_LIBVIRT_MEM_MB / 1024 ))"

How would this work on cloud (non-libvirt) systems?

-- 
Chuck Lever