Message-ID: <43FCDC88.7090602@wolfmountaingroup.com>
Date: Wed, 22 Feb 2006 14:50:00 -0700
From: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>
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To: Andrew Morton <akpm@osdl.org>
Cc: Robin Holt <holt@sgi.com>, john@johnmccutchan.com,
       linux-kernel@vger.kernel.org, rml@novell.com, arnd@arndb.de, hch@lst.de
Subject: Re: udevd is killing file write performance.
References: <20060222134250.GE20786@lnx-holt.americas.sgi.com>	<1140626903.13461.5.camel@localhost.localdomain>	<20060222175030.GB30556@lnx-holt.americas.sgi.com> <20060222120547.2ae23a16.akpm@osdl.org>
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Andrew Morton wrote:

>Robin Holt <holt@sgi.com> wrote:
>  
>
>>Let me reiterate, I know _VERY_ little about filesystems.  Can the
>> dentry->d_lock be changed to a read/write lock?
>>    
>>
>
>Well, it could, but I suspect that won't help - the hold times in there
>will be very short so the problem is more likely acquisition frequency.
>
>However it's a bit strange that this function is the bottleneck.  If their
>workload is doing large numbers of reads or writes from large numbers of
>processes against the same file then they should be hitting heavy
>contention on other locks, such as i_sem and/or tree_lock and/or lru_lock
>and others.
>
>Can you tell us more about the kernel-visible behaviour of this app?
>  
>

I have also seen this problem, and it's hard to reproduce. What you will 
see is udev getting spawned
multiple times as reported by top. I have found its related to 
intermittent failures of the hard drive and
the hotpluger for some reason invoking udev multiple times in response 
to this. I saw it on a Compaq
laptop right before my hard drive croaked, and it seems BIOS specific as 
well, since I have never seen
it or been able to reproduce it reliably.

Jeff

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