From: Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>
To: Rui Machado <ruimario-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Ralph Campbell
<ralph.campbell-h88ZbnxC6KDQT0dZR+AlfA@public.gmane.org>,
linux-rdma <linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: yet again the atomic operations
Date: Fri, 06 Aug 2010 08:49:16 -0700 [thread overview]
Message-ID: <adaocdf2137.fsf@roland-alpha.cisco.com> (raw)
In-Reply-To: <AANLkTimVTjHOubAaJ5oRHju6C7k7FZMqqq0Mvb4SBztB-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> (Rui Machado's message of "Fri, 6 Aug 2010 13:43:22 +0200")
> So if the CPU writes/reads to/from the same address, even atomically
> (lock), there might be room for some inconsistency on the values? It
> is not really atomic from the whole system point of view, just for the
> HCA? If so, is there any possibility to make the whole operation
> 'system-wide' atomic?
PCI does not have any capability for atomic operations until PCI Express
3.0 (not available in any real devices yet). So any current HCA
performing atomic operations across a PCI bus will always have to do
read-modify-write which leaves a window for the CPU to mess things up if
it accesses the same location.
You can work around this by creating a loopback connection (ie an RC
connection from the local HCA to itself) and post atomic operations to
that QP instead of accessing the memory directly with the CPU.
- R.
--
Roland Dreier <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> || For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/index.html
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next prev parent reply other threads:[~2010-08-06 15:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-04 12:32 yet again the atomic operations Rui Machado
[not found] ` <AANLkTikQX+CKvs_pjkH_Ap358jfjp4dYKYyKG95+eZmt-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-08-05 18:41 ` Ralph Campbell
[not found] ` <1281033688.7414.30.camel-/vjeY7uYZjrPXfVEPVhPGq6RkeBMCJyt@public.gmane.org>
2010-08-06 11:43 ` Rui Machado
[not found] ` <AANLkTimVTjHOubAaJ5oRHju6C7k7FZMqqq0Mvb4SBztB-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-08-06 15:49 ` Roland Dreier [this message]
[not found] ` <adaocdf2137.fsf-BjVyx320WGW9gfZ95n9DRSW4+XlvGpQz@public.gmane.org>
2010-08-10 11:50 ` Rui Machado
2010-08-06 17:26 ` Ralph Campbell
2010-08-10 11:46 ` Rui Machado
[not found] ` <AANLkTikPAqopgFR_vSnj9qkQu77S1RWixgM0POUQ5LM9-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-08-10 17:26 ` Ralph Campbell
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