RELENG_10 performance regression (was Re: 35-40% performance drop releng9 vs releng10 openvpn

[Mike Tancsa]

On 3/20/2015 8:15 PM, Konstantin Belousov wrote:
>>
>> For the purpose of devfs, does it make sense to bump timestamps like
>> normal filesystems for each read/write operation?  Looks like Mac OS X
>> will bump timestamps for each operation but Debian don't.
>
> First question is, what timecounter hardware is used.  I would accept
> some slowdown from hardware like HPET, but it is indeed surprising
> if caused by TSC.
>
>

David Wolfskill suggested trying the problem commit with

vfs.timestamp_precision=0

and it does indeed restore performance to what it was.  The raw dtrace 
files are available and FlameGraphs can all be found at

http://tancsa.com/time/

	---Mike
-- 
-------------------
Mike Tancsa, tel +1 519 651 3400
Sentex Communications, mike at sentex.net
Providing Internet services since 1994 www.sentex.net
Cambridge, Ontario Canada   http://www.tancsa.com/