linux-kernel - Re: [PATCH] block: export SSD/non-rotational queue flag through sysfs

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Message-ID: <Pine.LNX.4.64.0901152341500.15035@blonde.anvils>
Date:	Thu, 15 Jan 2009 23:50:13 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
cc:	Grant Grundler <grundler@...gle.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Greg Freemyer <greg.freemyer@...il.com>,
	Tejun Heo <htejun@...il.com>, Michael Tokarev <mjt@....msk.ru>,
	Kay Sievers <kay.sievers@...y.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] block: export SSD/non-rotational queue flag through
 sysfs

On Thu, 15 Jan 2009, James Bottomley wrote:
> 
> OK, so they could be calculated on the fly in the elevators, I suppose.
> But what would the value be?  Right now we use the nonrotational flag to
> basically not bother with plugging (no point if no seek penalty) on
> certain events where we'd previously have waited for other I/O to join.
> But that's really a seek penalty parameter rather than the idea of read
> or write costing (although the elevators usually track these dynamically
> anyway ... as part of the latency calculations but not explicitly).

... not bother with plugging (no point if no seek penalty) ...

I thought there was considerable advantage to plugging writes
(in case they turn out to be adjacent) on current and older
generations of non-rotational storage?

Hugh
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