From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [RFC PATCH 1/5] lguest: mmap backing file
Date: Thu, 20 Mar 2008 10:24:15 -0500
Message-ID: <47E2819F.6060406@codemonkey.ws>
References: <200803201659.14344.rusty@rustcorp.com.au>	<200803201705.44422.rusty@rustcorp.com.au>
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Cc: kvm-devel <kvm-devel@lists.sourceforge.net>,
	lguest <lguest@ozlabs.org>, virtualization@lists.linux-foundation.org
To: Avi Kivity <avi@qumranet.com>
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Avi Kivity wrote:
> Anthony Liguori wrote:
>> Rusty Russell wrote:
>>  
>>> From: Paul TBBle Hampson <Paul.Hampson@Pobox.com>
>>>
>>> This creates a file in $HOME/.lguest/ to directly back the RAM and 
>>> DMA memory
>>> mappings created by map_zeroed_pages.
>>>       
>>
>> I created a test program recently that measured the latency of a 
>> reads/writes to an mmap() file in /dev/shm and in a normal 
>> filesystem.  Even after unlinking the underlying file, the write 
>> latency was much better with a mmap()'d file in /dev/shm.
>>   
>
> Surely the difference disappears once the pages have been faulted in?

I don't recall.  I believe rewrite was okay but initial write was much 
worse.

Regards,

Anthony Liguori



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