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From: Nadia Derbey <Nadia.Derbey@bull.net>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 6/6] automatic tuning applied to some kernel components
Date: Tue, 23 Jan 2007 15:40:16 +0100	[thread overview]
Message-ID: <45B61E50.6020607@bull.net> (raw)
In-Reply-To: <20070122115638.835b26a1.akpm@osdl.org>

Andrew Morton wrote:
>>On Tue, 16 Jan 2007 07:15:22 +0100 Nadia.Derbey@bull.net wrote:
>>The following kernel components register a tunable structure and call the
>>auto-tuning routine:
>>  . file system
>>  . shared memory (per namespace)
>>  . semaphore (per namespace)
>>  . message queues (per namespace)
> 
> 
> This is the part of the patch series which really matters, and I just don't
> understand it :(
> 
> Why do we want to autotune these things?  What problem is this patch series
> solving?  Please describe this part of the work much, much more completely,
> so we can understand the need to add such a large amount of code to the
> kernel.

1) why these tunables?
The ipc tunables have been selected as "guinea-pig" tunables for the AKT 
framework because they are likely to be often used in data bases. This 
applies to file-max too.
Now, if the framework itself is accepted, the set of impacted tunables 
can easily be enhanced.

2) why autotuning:
There are at least 3 cases where it can be useful
. for workloads that are known to need a big amount of a given resource 
type (say shared memories), but we don't know what the maximum amount 
needed will be
. to solve the case of multiple applications running on a single system, 
and that need the same tunable to be adjusted to feet their needs
. to make a system correctly react to eventual peak loads for a given 
resource usage, i.e. make it tune up *and down* as needed.

In all these cases, the akt framework will enable the kernel to adapt to 
increasing / decreasing resource consumption:
1) avoid allocating "a priori" a big amount of memory that will be used 
only in extreme cases. This is the effect of doing an "echo <huge_value> 
 > /proc/sys/kernel/shmmni"
2) the system will come back to the default values as soon as the peak 
load is over.

> 
> It seems strange that the whole feature is Kconfigurable.  Please also
> explain the thinking behind that.

We wanted to make it configurable because it adds some overhead in terms of
1) generated kernel size
2) instructions added to the resource creation / removal code paths even 
if auto-tuning is not activated for th corresponding tunable -> 
performance impact.

> 
> I suspect the patches would be much simpler if you simply required that all
> these new tunables be of type `long'.  About seven eighths of the code
> would go away.  As would most of those eye-popping macros.
> 

Yes, agree with you: the idea here was to make the framework more 
generic. But I can change that.

Regards,
Nadia





  reply	other threads:[~2007-01-23 14:37 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-16  6:15 [RFC][PATCH 0/6] Automatice kernel tunables (AKT) Nadia.Derbey
2007-01-16  6:15 ` [RFC][PATCH 1/6] Tunable structure and registration routines Nadia.Derbey
2007-01-25  0:32   ` Randy Dunlap
2007-01-25 16:26     ` Nadia Derbey
2007-01-25 16:34       ` Randy Dunlap
2007-01-25 17:01         ` Nadia Derbey
2007-01-16  6:15 ` [RFC][PATCH 2/6] auto_tuning activation Nadia.Derbey
2007-01-16  6:15 ` [RFC][PATCH 3/6] tunables associated kobjects Nadia.Derbey
2007-01-16  6:15 ` [RFC][PATCH 4/6] min and max kobjects Nadia.Derbey
2007-01-24 22:41   ` Randy Dunlap
2007-01-25 16:34     ` Nadia Derbey
2007-01-16  6:15 ` [RFC][PATCH 5/6] per namespace tunables Nadia.Derbey
2007-01-24 22:41   ` Randy Dunlap
2007-01-16  6:15 ` [RFC][PATCH 6/6] automatic tuning applied to some kernel components Nadia.Derbey
2007-01-22 19:56   ` Andrew Morton
2007-01-23 14:40     ` Nadia Derbey [this message]
2007-02-07 21:18       ` Eric W. Biederman
2007-02-09 12:27         ` Nadia Derbey
2007-02-09 18:35           ` Eric W. Biederman
2007-02-13  9:06             ` Nadia Derbey
2007-02-13 10:10               ` Eric W. Biederman
2007-02-15  7:07                 ` Nadia Derbey
2007-02-15  7:49                   ` Eric W. Biederman
2007-02-15  8:25                     ` Nadia Derbey
2007-02-14 13:56 Al Boldi

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