svn commit: r242847 - in head/sys: i386/include kern

[Alfred Perlstein]

On 11/10/12 11:33 PM, Alexey Dokuchaev wrote:
> On Sat, Nov 10, 2012 at 10:22:52PM -0800, Peter Wemm wrote:
>> We've had kern.ipc.nmbclusters for years.  It is simple to understand,
>> easy to predict the outcome of a change, is runtime adjustable, is a
>> *cap* and not a reservation (like it used to be) and does not require
>> a reboot like maxusers tweaking would, and doesn't change maxproc as a
>> side effect.
>>
>> Tune the caps sensibly by default and move on.  maxusers must die.
> Big +1.  I would also like to get rid of maxusers altogether.
>
> ./danfe
You aren't really understanding it.

The contrived examples Peter are giving are *wrong*.
> Q: "How do I get an extra 2MB of clusters?"
> A1: "increase kern.ipc.nmbclusters by 1000"
> A2: "well, 2MB is 1000 clusters, and since you have mode than 768M of
> ram, you divide that 1000 clusters by 16 to get 62, then multiply that
> by 8 to reverse the maxusers slope factor above 768M, so you need to
> find the maxusers value you have and add 496 to it.  That will
> probably increase your clusters by 2MB. Maybe."
I am 100% aware that nmbclusters can override maxusers values, in fact 
it does.

The real conversation goes like this:

user: "Why is my box seeing terrible network performance?"
bsdguy: "Increase nmbclusters."
user: "what is that?"
bsdguy: "Oh those are the mbufs, just tell me your current value."
user: "oh it's like 128000"
bsdguy: "hmm try doubling that, go sysctl kern.ipc.nmbclusters=512000 on 
the command line."
user: "ok"
.... an hour passes ...
user: "hmm now I can't fork any more copies of apache.."
bsdguy: "oh, ok, you need to increase maxproc for that."
user: "so sysctl kern.ipc.maxproc=10000?"
bsdguy: "no... one second..."
....
bsdguy: "ok, so that's sysctl kern.maxproc=10000"
user: "ok... bbiaf"
....
user: "so now i'm getting log messages about can't open sockets..."
bsdguy: "oh you need to increase sockets bro... one second..."
user: "sysctl kern.maxsockets?"
bsdguy: "oh no.. it's actually back to kern.ipc.maxsockets"
user: "alrighty then.."
....
....
bsdguy: "so how is freebsd since I helped you tune it?"
user: "well i kept hitting other resource limits, boss made me switch to 
Linux, it works out of the box and doesn't require an expert tuner to 
run a large scale server.  Y'know as a last ditch effort I looked around 
for this 'maxusers' thing but it seems like some eggheads retired it and 
instead of putting my job at risk, I just went with Linux, no one gets 
fired for using Linux."
bsdguy: "managers are lame!"
user: "yeah!  managers..."

-Alfred