From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.com>
Subject: Re: raid10.c read_balance question
Date: Tue, 22 Nov 2016 15:49:05 +1100
Message-ID: <87h970ce66.fsf@notabene.neil.brown.name>
References: <CAANLjFodaUUZrROncC+uQjWX5pXVxgJ0HWkNunwugQQrp4Kojw@mail.gmail.com>
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To: Robert LeBlanc <robert@leblancnet.us>, linux-raid@vger.kernel.org
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On Tue, Nov 22 2016, Robert LeBlanc wrote:

> I'm looking to improve 'near' layout performance in raid10 and looking
> at the code for read_balance, the comments mention that there is a
> 'next expected sequential IO' sector number stored for the RAID array,
> but I don't see such a variable in the struct, nor do I see in
> read_balance where that variable is being updated. With such a value,
> I could use it (with another variable) to guess if the current
> requests are random or sequential enough to take the latency hit to
> move drive heads to help parallel the read. This would be a much
> simpler route than what I was thinking about previously.
>
> Am I just missing this variable? I would expect it to be in the
> r10conf struct, would that be the right place to implement it if
> doesn't exist?

I think it is "head_position".

NeilBrown

>
> Thanks,
> ----------------
> Robert LeBlanc
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