linux-kernel - Re: Higher than expected disk write(2) latency

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Message-ID: <20080710134144.GA31461@dezo.moloch.sk>
Date:	Thu, 10 Jul 2008 15:41:46 +0200
From:	Martin Lucina <mato@...elna.sk>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Martin Sustrik <sustrik@...tmq.com>,
	linux-kernel@...r.kernel.org, linux-aio@...ck.org
Subject: Re: Higher than expected disk write(2) latency

chris.mason@...cle.com said:
> Is NCQ enabled on the drive?  The basic way to fix this is to have
> multiple requests in flight, which isn't going to happen on sata with
> the cache off and with ncq off.

ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
ata1.00: ATA-7: Hitachi HDS721616PLA380, P22OAB3A, max UDMA/133
ata1.00: 321672960 sectors, multi 0: LBA48 NCQ (depth 31/32)
ata1.00: configured for UDMA/133

I'm assuming the above indicates NCQ is enabled.

We'll try running the tests tomorrow with different i/o schedulers and
report back.

-mato
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