High rate of NFS cache misses after upgrading from 10.3-prerelease to 11.1-release

[Eugene Grosbein]

15.04.2018 21:19, Rodney W. Grimes wrote:

>>>> It is a website with quite some traffic handles by three webservers behind a pair >of loadbalancers.
>>>> We see a loss of 20% in speed(TTFB reduced by 100ms; sounds not a lot but >Google et al doesn?t like it at all) after upgrading to 11.1 with a combined upgrade >to php7.1. On another server without NFS that upgrade improved performance >considerably (I was told ca 30% by the front end-dev)
>>> One thing you could try is booting the 11.1 kernel on an 10.3 system. Newer
>>> FreeBSD kernels should work with older userland.
>>
>> Though one should remember that some important system utilities
>> may and probably will not work with newer kernel, like /sbin/ipfw, route,
>> ifconfig, netstat etc.
> 
> I thought that as long as the newer kernel has the right
> COMPAT_FREEBSD10 compiled in that all this stuff should work.
> Am I miss understanding this kernel option?

COMPAT_FREEBSD10 does not cover all cases (in-kernel structures etc.)
and bugs can happen, too. You won't be happy if you discover
similar case in /sbin/ipfw or ifconfig as this combination (old ipfw+new kernel)
is not something we test thoroughly.