linux-kernel - Re: [PATCH] replace ida in workqueue with page-sized buffer

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Message-ID: <20110108140136.GA13269@mtj.dyndns.org>
Date:	Sat, 8 Jan 2011 09:01:36 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] replace ida in workqueue with page-sized buffer

Hello,

On Sat, Dec 18, 2010 at 09:10:18PM +0800, Hillf Danton wrote:
> The id of worker of global work queue is monitored with kernel library, ida.
> 
> The ida in global work queue is redefined to be page-sized buffer,
> which is allocated when initializing workqueue.
> 
> The new id allocator could monitor ids in the rage from 0 to INT_MAX.
> The buffer is used to store freed ids, and if the peak number of ids,
> in workqueue as whole, is not out of the capacity of the allocated
> buffer, there is no more allocation of buffer after initializing.
> 
> The advantage looks that the new allocator runs faster.

I'm confused about why this is necessary.  It's not like workqueue ID
alloc/dealloc is hot path to begin with (they're quite lazy) and
during worker creation / destruction ida is a quite insignificant
part, so what is it trying to optimize?  It's not like ida allocator
is slow to begin with.

Also, the allocator looks quite dubious.

* What happens if more entries than what can fit in a page are freed?
  It'll just lose track of it.

* ida guarantees that always the lowest available slot is allocated.
  The new allocator doesn't.

So, why oh why?

-- 
tejun
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