linux-kernel - Re: [ckrm-tech] [RFC][PATCH 2/7] UBC: core (structures, API)

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Date:	Mon, 21 Aug 2006 15:02:17 +0400
From:	Kirill Korotaev <dev@...ru>
To:	Matt Helsley <matthltc@...ibm.com>
CC:	"Chandra S. Seetharaman" <sekharan@...ibm.com>,
	Rik van Riel <riel@...hat.com>,
	CKRM-Tech <ckrm-tech@...ts.sourceforge.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Christoph Hellwig <hch@...radead.org>,
	Andrey Savochkin <saw@...ru>, devel@...nvz.org,
	hugh@...itas.com, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Emelianov <xemul@...nvz.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [ckrm-tech] [RFC][PATCH 2/7] UBC: core (structures, API)

>>>>+	for (p = ub; p != NULL; p = p->parent) {
>>>
>>>
>>>Seems rather expensive to walk up the tree for every charge. Especially
>>>if the administrator wants a fine degree of resource control and makes a
>>>tall tree. This would be a problem especially when it comes to resources
>>>that require frequent and fast allocation.
>>
>>in heirarchical accounting you always have to update all the nodes :/
>>with flat UBC this doesn't introduce significant overhead.
> 
> 
> Except that you eventually have to lock ub0. Seems that the cache line
> for that spinlock could bounce quite a bit in such a hot path.
do you mean by ub0 host system ub which we call ub0
or you mean a top ub?

> Chandra, doesn't Resource Groups avoid walking more than 1 level up the
> hierarchy in the "charge" paths?

Kirill

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