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

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Date:	Mon, 14 Apr 2008 10:33:23 +0200
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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

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




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