Re: An interesting anomaly in NFS client...

On Nov 7, 2024, at 2:09 PM, Mark Johnston <[email protected]> wrote:
> 
> On Thu, Nov 07, 2024 at 07:28:59AM +0200, Andriy Gapon wrote:
>> On 07/11/2024 02:43, George Neville-Neil wrote:
>>> Howdy,
>>> 
>>> We've been digging into an interesting possible issue in the FreeBSD NFS
>>> client. Here is the scenario. I have a FreeBSD VM on my Mac, the Mac is
>>> the NFS server, the VM is the client. I then attempt to build an out of
>>> tree kernel module that I'm working on. The build looks like it's
>>> hanging for 1.5 seconds, and when we look at the packets (pcap file
>>> attached) we see a ton of GETATTRs over the first 1.5 seconds. I've put
>>> the pcap up here: oct_8_2024.pcapng <https://
>>> people.freebsd.org/~gnn/oct_8_2024.pcapng>
>>> 
>>> I also note that an issue was raised on the forums that seems similar,
>>> way back between FreeBSD 10 and 11:
>>> 
>>> https://forums.freebsd.org/threads/nfs-cache-misses-after-upgrading-to-11-1-
>>> from-10-3.65491/
>>> <https://forums.freebsd.org/threads/nfs-cache-misses-after-
>>> upgrading-to-11-1-from-10-3.65491/>
>>> 
>>> I'm seeing this on 15 currentish (last few months).
>> 
>> Could it be just make checking for stale targets?
>> I.e., stat-ing various files to check their timestamps.
> 
> I suspect it is from this line in sys/conf/config.mk:
> 
> __MPATH!=find ${SYSDIR:tA}/ -name \*_if.m
> 
> This is running a find command over all of sys/, so it'll stat about
> 35000 files.  I believe it's from
> https://cgit.freebsd.org/src/commit/?id=12f05b84463baacfada5a79eaed061a4899d98aa

At least for this find, p9fs (in freebsd vm) is about 20 times faster!
No idea how well qemu's 9pfs works but worth a try.