linux-kernel - RE: [ia64] Question on __ARCH_WANT_UNLOCKED

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Date:	Wed, 24 Aug 2011 13:46:58 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ken Chen <kenchen@...gle.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	David Miller <davem@...emloft.net>
Subject: RE: [ia64] Question on __ARCH_WANT_UNLOCKED_CTXSW

> happen to remember what the perceived benefit of using
> __ARCH_WANT_UNLOCKED_CTXSW was about?

No - digging around the code hasn't rung any bells for me either.

Perhaps just general goodness for not holding a lock for
longer than we need to?  But that would imply some case where
someone else could do something useful by being able to grab
the lock when we drop it. About the only thing I can think
of is that it would allow tasks to be re-balanced just a
teeny bit earlier --- but re-balancing ought to be somewhat
rare, yes?

-Tony