Date: Thu, 15 Jan 2009 23:50:13 +0000 (GMT)
From: Hugh Dickins <hugh@veritas.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
cc: Grant Grundler <grundler@google.com>, Jens Axboe <jens.axboe@oracle.com>,
       Greg Freemyer <greg.freemyer@gmail.com>, Tejun Heo <htejun@gmail.com>,
       Michael Tokarev <mjt@tls.msk.ru>, Kay Sievers <kay.sievers@vrfy.org>,
       Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>,
       linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH] block: export SSD/non-rotational queue flag through
 sysfs
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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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