From: David Mosberger <davidm@napali.hpl.hp.com>
To: linux-ia64@vger.kernel.org
Subject: Re: [PATCH_TAKE_2] now < last_tick problem
Date: Mon, 13 Oct 2003 18:17:06 +0000 [thread overview]
Message-ID: <marc-linux-ia64-106606930611851@msgid-missing> (raw)
In-Reply-To: <marc-linux-ia64-106575925709435@msgid-missing>
>>>>> On Mon, 13 Oct 2003 12:11:52 +1000, Ian Wienand <ianw@gelato.unsw.edu.au> said:
Ian> Well, to my eyes the use of the xtime_lock in do_gettimeofday() looks
Ian> OK, but I guess what you are saying is that the message is moot --
Ian> xtime_lock protects everything itc_get_offset() needs, and
Ian> do_gettimeofday() has a read lock on xtime_lock and so reads the
Ian> offset again if something was updated underneath it.
You do realize that xtime_lock is NOT a lock at all? Seqlock is a
scheme for lock-free synchronization. Readers and writers will run
concurrently and the only guarantee that you get is that if a writer
interfered with a reader, the reader will retry its operation (but of
course, this means that the reader occasionally will be seeing
inconsistent data).
--david
next prev parent reply other threads:[~2003-10-13 18:17 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-10 4:13 [PATCH_TAKE_2] now < last_tick problem Ian Wienand
2003-10-10 16:42 ` David Mosberger
2003-10-13 2:11 ` Ian Wienand
2003-10-13 18:17 ` David Mosberger [this message]
2003-10-13 23:06 ` Ian Wienand
2003-10-14 5:23 ` David Mosberger
2003-10-14 5:53 ` Ian Wienand
2003-10-14 16:58 ` David Mosberger
2003-10-14 23:05 ` Ian Wienand
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