Date: Mon, 27 Mar 2000 00:48:12 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Mike Smith <msmith@FreeBSD.ORG> Cc: Warner Losh <imp@village.org>, Mike Smith <msmith@FreeBSD.ORG>, Daniel Eischen <eischen@vigrid.com>, nms@otdel-1.org, freebsd-current@FreeBSD.ORG Subject: Re: Is there spinlocks/semaphores available for drivers? Message-ID: <200003270848.AAA37083@apollo.backplane.com> References: <200003270720.XAA05430@mass.cdrom.com>
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:> In message <200003270639.WAA05313@mass.cdrom.com> Mike Smith writes:
:> : What about it in particular? Or are you referring to overflow handling?
:>
:> Yes. Well, I guess I assumed it was a circular thing, and you'd need
:> to have some comparison against read index, which would be racible.
:
:Not if you think about it; all you need are atomic read/write operations
:for the indexes. Circular FIFOs are kinda neat like that. 8)
:
:--
:\\ Give a man a fish, and you feed him for a day. \\ Mike Smith
Well, monotonically increasing (except when it wraps), and atomic
writes. Atomic read-modify-writes are not required which means that
no locking is needed at all, not even a 'lock' prefix (though on some
architectures you have to worry about delayed commits between cpu's).
-Matt
Matthew Dillon
<dillon@backplane.com>
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