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From: Tejun Heo <>
To: Jens Axboe <>, Jeff Garzik <>,
	Linus Torvalds <>,
	IDE/ATA development list <>,
	Linux Kernel <>
Subject: request to revert libata-convert-to-block-tagging patches
Date: Mon, 10 Nov 2008 14:19:05 +0900	[thread overview]
Message-ID: <> (raw)

Hello, all.

I went through libata-convert-to-block-tagging today and found several

1. libata internal data structure for command context (qc) allocation is
bound to tag allocation, which means that block layer tagging should be
enabled for all controllers which have can_queue > 1.

2. blk-tag offsets allocation for non-sync requests.  I'm not confident
this is safe.  Till now, if there was only single command in flight for
the port, it was guaranteed that the qc gets tag zero whether the device
is NCQ capable or not.  qc allocation is tied tightly with hardware
command slot allocation and I don't think it's wise to change this

#1 is easy to fix but #2 requires either adding a spinlock or two atomic
variables to struct blk_queue_tag to keep the current behavior while
guaranteeing that tags are used in order.  Also, there's delay between
libata marks a request complete and the request actually gets completed
and the tag is freed.  If another request gets issued inbetween, the tag
number can't be guaranteed.  This can be worked around by re-mapping tag
number in libata depending on command type but, well then, it's worse
than the original implementation.

So, please revert the following commits.




             reply	other threads:[~2008-11-10  5:20 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-10  5:19 Tejun Heo [this message]
2008-11-10  5:30 ` Tejun Heo
2008-11-10  5:48   ` [PATCH] libata: revert convert-to-block-tagging patches Tejun Heo
2008-11-10 12:05 ` request to revert libata-convert-to-block-tagging patches Jens Axboe
2008-11-10 12:09   ` Jens Axboe
2008-11-10 16:00     ` Linus Torvalds
2008-11-10 17:10       ` Jens Axboe
2008-11-10 13:24   ` Tejun Heo
2008-11-10 16:03     ` Linus Torvalds
2008-11-10 22:55 ` Jeff Garzik
2008-11-12  1:11   ` Linus Torvalds

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