linux-kernel - Re: [PATCH 00/13] Re: Scalability requirements for sysv ipc

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Date:	Mon, 14 Apr 2008 12:52:12 +0200
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Nadia Derbey <Nadia.Derbey@...l.net>
Cc:	Peter Zijlstra <peterz@...radead.org>, efault@....de,
	manfred@...orfullife.com, linux-kernel@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	xemul@...nvz.org
Subject: Re: [PATCH 00/13] Re: Scalability requirements for sysv ipc

Nadia Derbey wrote:
> Peter Zijlstra wrote:
> 
>> On Mon, 2008-04-14 at 07:18 +0200, Nadia Derbey wrote:
>>
>>> Peter Zijlstra wrote:
>>>
>>>> On Fri, 2008-04-11 at 18:17 +0200, Nadia.Derbey@...l.net wrote:
>>>>
>>>>
>>>>> Here is finally the ipc ridr-based implementation I was talking 
>>>>> about last
>>>>> week (see http://lkml.org/lkml/2008/4/4/208).
>>>>> I couldn't avoid much of the code duplication, but at least made 
>>>>> things
>>>>> incremental.
>>>>>
>>>>> Does somebody now a test suite that exists for the idr API, that I 
>>>>> could
>>>>> run on this new api?
>>>>>
>>>>> Mike, can you try to run it on your victim: I had such a hard time 
>>>>> building
>>>>> this patch, that I couldn't re-run the test on my 8-core with this new
>>>>> version. So the last results I have are for 2.6.25-rc3-mm1.
>>>>>
>>>>> Also, I think a careful review should be done to avoid introducing 
>>>>> yet other
>>>>> problems :-(
>>>>
>>>>
>>>>
>>>> Why duplicate the whole thing, when we converted the Radix tree to be
>>>> RCU safe we did it in-place. Is there a reason this is not done for 
>>>> idr?
>>>>
>>>>
>>>>
>>>
>>> I did that because I wanted to go fast and try to fix the performance 
>>> problem we have with sysV ipc's. I didn't want to introduce (yet 
>>> other) regressions in the code that uses idr's today and that works 
>>> well ;-)
>>> May be in the future if this rcu based api appears to be ok, we can 
>>> replace one with the other?
>>
>>
>>
>>> From what I can see the API doesn't change at all,
> 
> 
> Well, 1 interface changes, 1 is added and another one went away:
> 
> 1) for the preload part (it becomes like the radix-tree preload part):
> 
> int idr_pre_get(struct idr *, gfp_t);
> would become
> int idr_pre_get(gfp_t);
> 
> 2) idr_pre_get_end() is added (same as radix_tree_preload_end()).
> 
> 3) The idr_init() disappears.
> 
> You might see that other interfaces are not provided by ridr, but this 
> is only because I've taken those that are useful for the ipc part (so 
> should not be a problem to make the whole thing rcu safe).
> 
>> so I don't see why
>> you need to duplicate - either the new code works as expected or its
>> broken.
> 
> 
> That's why I asked for an "IDR test suite": I wanted to test potential 
> regressions.
> 
>> If it works its good enough for all IDR users, if its broken we
>> should fix it. Seems simple enough.. am I missing something obvious?
>>
> 
> Regards,
> Nadia
> 

BTW, I'm realizing that I forgot to send the results I've got - sorry 
for that (I finally could pass the pmsg/psem tests this morning):

These are the output files for the command:

for i in 1 2 3 4 5 6 7 8;do ./pmsg $i 5;done

pmsg_output.25_rc8_mm1.ref.8: output file for the 2.6.25-rc8-mm1
                               reference kernel
pmsg_output.25_rc8_mm1.ridr.8: output file for the 2.6.25-rc8-mm1
                                refrence kernel, with ipc's using
                                rcu-based idr's
psem_output.25_rc8_mm1.ref.8: same as <1> for the psem test
psem_output.25_rc8_mm1.ridr.8: same as <2> for the psem test

Regards,
Nadia


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