From: "Jan Beulich" <JBeulich@suse.com>
To: "Dexuan Cui" <decui@microsoft.com>
Cc: "jeremy@goop.org" <jeremy@goop.org>,
"KY Srinivasan" <kys@microsoft.com>,
"chrisw@sous-sol.org" <chrisw@sous-sol.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: sync_set_bit() vs set_bit() -- what's the difference?
Date: Wed, 27 Aug 2014 08:38:35 +0100 [thread overview]
Message-ID: <53FDA71B020000780002DF2E@mail.emea.novell.com> (raw)
In-Reply-To: <EE124450C0AAF944A40DD71E61F878C99639F3@SINEX14MBXC419.southpacific.corp.microsoft.com>
>>> On 27.08.14 at 09:30, <decui@microsoft.com> 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?
I guess this would really want to be used by anything communicating
with a hypervisor or a remote driver: set_bit() gets its LOCK prefix
discarded when the local kernel determines it runs on a single CPU
only. Obviously having knowledge of the CPU count inside a VM does
not imply anything about the number of CPUs available to the host,
i.e. stripping LOCK prefixes in that case would be unsafe.
Jan
next prev parent reply other threads:[~2014-08-27 7:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-27 7:30 sync_set_bit() vs set_bit() -- what's the difference? Dexuan Cui
2014-08-27 7:38 ` Jürgen Groß
2014-08-27 7:38 ` Jan Beulich [this message]
2014-08-27 7:50 ` Dexuan Cui
2014-08-27 7:58 ` Jürgen Groß
2014-08-27 13:56 ` KY Srinivasan
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