Messages in this thread | | | Date | Fri, 20 Jan 2006 00:47:03 -0600 (CST) | From | Brent Casavant <> | Subject | Re: [PATCH] SN2 user-MMIO CPU migration |
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On Thu, 19 Jan 2006, Jesse Barnes wrote:
> Maybe you could just turn the above into mmiowb() calls instead? That > would cover altix, origin, and ppc as well I think. On other platforms > it would be a complete no-op.
As you obviously noted, the core of the code was lifted from mmiowb(). But no, an mmiowb() as such isn't correct. At the time this code is executing, it's on a CPU remote from the one which issued any PIO writes to the device. So in this case we need to poll the Shub register for a remote node, but mmiowb() only polls for the Shub corresponding to the current CPU.
My first incarnation of this patch (never publicly presented) did implement a new mmiowb_remote(cpu) machvec instead, and this was placed in the context-switch (in) path instead of the task migration path. However, since this behavior is only needed for the task migration case, Jack Steiner pointed out that this was a more appropriate way to implement it. As migration is much less frequent than context switching, this is a better-performing method to solve the problem.
Thanks, Brent
-- Brent Casavant All music is folk music. I ain't bcasavan@sgi.com never heard a horse sing a song. Silicon Graphics, Inc. -- Louis Armstrong - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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