linux-kernel - Re: root=PARTUUID for MBR/NT disk signatures?

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Message-ID: <50332CEF.7010204@msgid.tls.msk.ru>
Date:	Tue, 21 Aug 2012 10:38:39 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	Will Drewry <wad@...omium.org>
CC:	Stephen Warren <swarren@...dotorg.org>, Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cross-distro@...ts.linaro.org" <cross-distro@...ts.linaro.org>,
	Jens Axboe <axboe@...nel.dk>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: root=PARTUUID for MBR/NT disk signatures?

On 21.08.2012 08:47, Will Drewry wrote:
[]
> Functionally, I suspect this will work fine, but I am concerned that
> it is a bad move from an efficiency perspective (not unfixable
> though).  Right now, the user-supplied value is converted from
> string-uuid to packed-uuid.  This is then memcmp'd across any and all
> partitions - be it 2 or 200 - across all attached storage.  If we move
> to a pure string, then we end up needing to unpack every packed UUID
> at disk scan time (or search, depending on impl) rather than just the
> one user supplied value.
> 
> Perhaps the cost is negligible on modern machines, but it seems like
> the wrong place to put the cost (per entry rather than per search
> value).

Amount of work needed to READ all the partition tables might be
quite a bit larger than strcmp'ing it all.  I think.

/mjt
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