Re: Poor performance of pthreads across cpu dies.
Re: Poor performance of pthreads across cpu dies.
- Subject: Re: Poor performance of pthreads across cpu dies.
- From: Terry Lambert <email@hidden>
- Date: Wed, 5 Sep 2007 12:50:01 -0700
On Sep 5, 2007, at 6:26 AM, Andrew Gallatin wrote:
Terry Lambert writes:
On Sep 4, 2007, at 6:09 AM, Andrew Gallatin wrote:
The *NIC* has looked at it, and can easily hash different
connections
to several MSI-X interrupt handlers, which are then each bound to
different CPUs (or groups of CPUs).
I am told we support this (Message Signalled Interrupts) for the
latest Intel OS releases, and that it is in fact the preferred method
of interrupt delivery these days, for hardware capable of supporting
it. I wasn't able to find the tech note, which is supposed to have
been published already, according to the author, so you might want to
contact DTS.
MSI is different from MSI-X. I figured out how to use MSI from the
headers / source last winter, but AFAIK, darwin/macosx does not yet
support MSI-X, which is required to have multiple interrupt vectors
per device which are bound to different CPUs.
Like I said, it's probably time to stop speculating, and ask DTS for
the Tech Note.
-
According to the public documentation available to me, the advantages
of MSI-X over MSI are:
- Support a larger maximum number of vectors per function
- Provide the ability for system software to configure each vector
with an independent message address and message data,
specified by a table that resides in Memory Space
- Per-vector masking is an optional extension of MSI but a required
feature for MSI-X.
From my reading of things, the issue as to whether or not you can
target multiple CPUs with MSI has more to do with contiguous vs. non-
contiguous vector assignment (which means that it's not possible in
older Linux kernels). The MSI-X implementation overcomes this in
older Linux kernels due to independent configuration of message data
and address. BUT, if you are willing to perform contiguous
allocations, it's not a problem for MSI to do the same.
NB: This is according to Tom L. Nguyen of Intel's "The MSI Driver
Guide HOWTO" for Linux, revised 12 Feb 2004 by Martine Silbermann of HP.
-- Terry
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