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Re: [Xen-devel] [PATCH] fix event channel notification loss on IA64

from [Keir Fraser]

[Permanent Link][Original]

To:	Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] fix event channel notification loss on IA64
From:	Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date:	Thu, 29 Jun 2006 14:28:37 +0100
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On 29 Jun 2006, at 06:43, Isaku Yamahata wrote:

evtchn_do_upcall() has a micro optimization which is depends on
that xchg is a barrier.
However xchg of IA64 has acquire semantics so that event
channel notification is lost sometimes. This patch fixes it.

clear_bit() isn't a barrier either (at least according to Linux bitopsemantics). You want 'rmb();'. I suggest just putting it inside ifndefCONFIG_X86, with the comment about XCHG being a barrier on x86 placedjust before the ifndef. Leave the zap of pending flag as a plain write.


 -- Keir


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