linux-kernel - Re: sync_set_bit() vs set_bit() -- what's the difference?

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Message-ID: <53FD8AF1.8010608@suse.com>
Date:	Wed, 27 Aug 2014 09:38:25 +0200
From:	Jürgen Groß <jgross@...e.com>
To:	Dexuan Cui <decui@...rosoft.com>,
	KY Srinivasan <kys@...rosoft.com>,
	"chrisw@...s-sol.org" <chrisw@...s-sol.org>,
	"jeremy@...p.org" <jeremy@...p.org>,
	Jan Beulich <JBeulich@...e.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: sync_set_bit() vs set_bit()  -- what's the difference?

On 08/27/2014 09:30 AM, Dexuan Cui wrote:
> I'm curious about the difference. :-)
>
> sync_set_bit() is only used in drivers/hv/ and drivers/xen/ while set_bit() is used in all other places. What makes hv/xen special?

In set_bit() the "lock" prefix will be dropped if only one processor is
present. sync_set_bit() is always attributed with "lock".

xen and hv might require "lock" semantics even if the current OS is
running on only one processor, as syncing with other processors running
other OS's might be necessary.

Juergen

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