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From: Andi Kleen <andi@firstfloor.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	"David Miller" <davem@davemloft.net>,
	"Arnaldo Carvalho de Melo" <acme@redhat.com>
Subject: Re: [RFC PATCH 8/8] Jhash in too big for inlining, move under lib/
Date: Sat, 23 Feb 2008 14:06:53 +0100	[thread overview]
Message-ID: <p738x1b95zm.fsf@bingen.suse.de> (raw)
In-Reply-To: <20080223000214.81b1390a.akpm@linux-foundation.org> (Andrew Morton's message of "Sat\, 23 Feb 2008 00\:02\:14 -0800")

Andrew Morton <akpm@linux-foundation.org> writes:
>
> It should be possible to use a modular jhash.ko.  The things which you
> have identified as clients of the jhash library are usually loaded as modules.

For very small functions like this own modules are quite expensive. First  
everything gets rounded up to at least one 4K page (or worse on architectures
with larger pages). That just wastes some memory. 

But then since modules live in vmalloc space they also need an own 
TLB entry, which are notouriously scarce in the kernel because often user space
wants to monopolize them all. So if you're unlucky and user space
is thrashing the TLB just a single call to this hash function will be an own 
TLB miss and quite expensive.

It would be better to just always link it in for this case.

-Andi

  parent reply	other threads:[~2008-02-23 13:07 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-20 13:47 [RFC PATCH 0/8]: uninline & uninline Ilpo Järvinen
2008-02-20 13:47 ` [RFC PATCH 1/8] [NET]: uninline skb_put, de-bloats a lot Ilpo Järvinen
2008-02-20 13:47   ` [RFC PATCH 2/8] [NET]: uninline skb_pull, " Ilpo Järvinen
2008-02-20 13:47     ` [RFC PATCH 3/8] [NET]: uninline dev_alloc_skb, " Ilpo Järvinen
2008-02-20 13:47       ` [RFC PATCH 4/8] [NET]: uninline skb_push, " Ilpo Järvinen
2008-02-20 13:47         ` [RFC PATCH 5/8] [NET]: uninline dst_release Ilpo Järvinen
2008-02-20 13:47           ` [RFC PATCH 6/8] [NET]: uninline skb_trim, de-bloats Ilpo Järvinen
2008-02-20 13:47             ` [RFC PATCH 7/8] [SCTP]: uninline sctp_add_cmd_sf Ilpo Järvinen
2008-02-20 13:47               ` [RFC PATCH 8/8] Jhash in too big for inlining, move under lib/ Ilpo Järvinen
2008-02-23  8:02                 ` Andrew Morton
2008-02-23 10:05                   ` Ilpo Järvinen
2008-02-23 18:21                     ` Andrew Morton
2008-02-23 13:06                   ` Andi Kleen [this message]
2008-02-20 22:16               ` [RFC PATCH 7/8] [SCTP]: uninline sctp_add_cmd_sf Vlad Yasevich
2008-02-20 22:34                 ` Ilpo Järvinen
2008-02-21 15:27                   ` Vlad Yasevich
2008-02-20 16:19       ` [RFC PATCH 3/8] [NET]: uninline dev_alloc_skb, de-bloats a lot Jan Engelhardt
2008-02-20 16:27         ` Patrick McHardy
2008-02-20 16:30           ` Jan Engelhardt
2008-02-20 22:18             ` Ilpo Järvinen
2008-03-12 15:27               ` Ilpo Järvinen
2008-02-20 13:54   ` [RFC PATCH 1/8] [NET]: uninline skb_put, " Patrick McHardy
2008-02-20 13:57   ` Eric Dumazet
2008-02-23  8:02 ` [RFC PATCH 0/8]: uninline & uninline Andrew Morton
2008-02-23 10:11   ` Ilpo Järvinen
2008-02-23 13:15   ` Andi Kleen
2008-02-23 18:06     ` Ilpo Järvinen
2008-02-23 18:55     ` Andrew Morton
2008-02-23 19:58       ` Hua Zhong
2008-02-23 21:02         ` Andi Kleen
2008-02-27 19:08       ` profile-likely patch (was " Valdis.Kletnieks

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