linux-kernel - Re: [PATCH] cfq-iosched: non-rot devices do not need read queue merging

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Message-Id: <E1NSq2i-0000wY-00.kirill_nnov-mail-ru@foot.mail.ru>
Date:	Thu, 07 Jan 2010 13:56:40 +0300
From:	Kirill Afonshin <kirill_nnov@...l.ru>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Jeff Moyer <jmoyer@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Shaohua Li <shaohua.li@...el.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>
Subject: Re: [PATCH] cfq-iosched: non-rot devices do not need read queue  merging

I think we should not rely on NCQ/non-NCQ or blk_queue_nonrot() because it may be incorrect:
try this:

find /sys/ -name rotational 2>/dev/null
find /sys/ -name rotational 2>/dev/null|xargs cat

all devices are reported as rotational for me including ram, loop and usb flash drive. Physical block size and optimal io size has invalid values for all my usb flash drives.

I think it would be better to do a short performance test before mount. It will provide all necessary information for io scheduler. We doesn't need information about NCQ and rotational. We need to predict how much time specific io operation will take in current context.

PS: I'm not native speaker.

Best regards,
Kirill Afonshin
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