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Re: concurrent direct IO write in xfs

To: Zheng Da <zhengda1936@xxxxxxxxx>
Subject: Re: concurrent direct IO write in xfs
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 16 Jan 2012 12:48:19 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <CAFLer83FBZG9ZCrT2jUZBcTC2a2tx_CDmykyPF4cTP0dbHGw7Q@xxxxxxxxxxxxxx>
References: <CAFLer83FBZG9ZCrT2jUZBcTC2a2tx_CDmykyPF4cTP0dbHGw7Q@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, Jan 15, 2012 at 07:01:42PM -0500, Zheng Da wrote:
> Hello,
> 
> I surprisedly found that writing data to a file (no appending) with direct
> IO and with multiple threads has the same performance as a single thread.
> Actually, it seems there is only one core is working at a time. In my case,
> each time I write a page to a file and the offset is always aligned to the
> page size, so there is no overlapping between writes.

What kernel version are you using?  Also, what is the exact I/O
pattern?

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