Date: Tue, 16 Jan 2001 12:37:59 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Mark Murray <mark@grondar.za> Cc: cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org, jake@FreeBSD.org, Matt Dillon <dillon@earth.backplane.com> Subject: Re: Atomic ops (Was Re: cvs commit: src/sys/i386/include atomic. Message-ID: <XFMail.010116123759.jhb@FreeBSD.org> In-Reply-To: <200101161826.f0GIPwI33543@gratis.grondar.za>
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On 16-Jan-01 Mark Murray wrote: >> A bottom half / top half circular FIFO does not need to use atomic ops >> at all. The writer simply manipulates the WIndex and the reader >> simply manipulates the RIndex. If you have multiple readers or >> multiple writers, then you have a locking issue, but if you don't there >> are no issues. > > I have multiple writers, and a single reader. Perhaps making the issue > easier is the fact that I don't mind losing harvested events, so if a > writer can't write, tough luck, do nothing and return. > >> On a non-intel box that does not guarentee write ordering, you would >> need a memory barrier function prior to updating the WIndex to >> ensure that the FIFO data is in place as of the time the reader tests >> its RIndex against the WIndex. > > This is the way I've got it, more-or-less. I'm hoping for a method that > does not involve memory barriers, if I can. I'm playing with ideas right > now. Only having 1 mb is better than having two. -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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