MD5 test slowdown

[Rafal Jaworowski]

On 2009-07-03, at 10:20, Kostik Belousov wrote:

> On Fri, Jul 03, 2009 at 02:04:50AM +0200, Max Laier wrote:
>> On Thursday 02 July 2009 13:32:08 Rafal Jaworowski wrote:
>>> I'm observing some heavy slowdown seen with md5 test on PowerPC:
>>>
>>> 1. On the MPC8572 machine with today's HEAD I'm getting:
>>>
>>> # md5 -t
>>> MD5 time trial. Digesting 100000 10000-byte blocks ... done
>>> Digest = 766a2bb5d24bddae466c572bcabca3ee
>>> Time = 36.930565 seconds
>>> Speed = 27077842.000000 bytes/second
>>>
>>> 2. While a couple of months back it yielded 6x shorter times on this
>>> very same hardware, like this one:
>>>
>>> # md5 -t
>>> MD5 time trial. Digesting 100000 10000-byte blocks ... done
>>> Digest = 766a2bb5d24bddae466c572bcabca3ee
>>> Time = 6.027277 seconds
>>> Speed = 165912400.000000 bytes/second
>>>
>>> Timers work fine, the slowdown is real. I don't know if this is
>>> PowerPC related, and was wondering if anybody observed something
>>> similar on other archs perhaps? Any suggestions what could be  
>>> causing
>>> this or where to look? I cannot see immediate suspects in the arch/
>>> platform code.
>>
>> "signifanctly slowdown of FreeBSD 8.0-CURRENT/amd64" to this  
>> mailing list
>> reports something that might be related.  It seems there is a patch
>> available, but not committed yet.  Though I'm not sure about the  
>> nature of
>> the problem exactly.  Jeff?
>
> I want to make some points clear to avoid a confusion and spread of  
> FUD.
> It seems we have at least three issues, all different:
> 1. Syscalls slowdown on amd64. To see this, you need to microbenchmark
>   syscall enter/leave sequence. I doubt that it can be seen on any
>   load except while (1) {getpid();} loops or such. The issue is valid
>   _only_ for amd64.
>   I developed the patch with the input from Jeff who confirmed that
>   this slowdown is solved by the change.
> 2. There are enough independent reports of i/o slowdown to believe  
> that
>   some problem is real; but we have not seen numbers or detailed
>   configurations or (most desirable) the revision after which the
>   slowdown started. Note the i/o part.
>
> This report is for PPC (right ?) and for workload that is purely
> CPU-bounded.

After additional testing my slowdown looks more like a PowerPC (E500  
only) issue: nwhitehorn@ checked his G4 (AIM) system and could not  
observe this, so it seems something local to E500.

Rafal