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Re: [Xen-devel] [PATCH] "lock cmpxch8b" and split locks

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] "lock cmpxch8b" and split locks
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 5 Oct 2005 23:02:31 +0100
Cc: "Koren, Bradley J" <Bradley.Koren@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, "Vessey, Bruce A" <Bruce.Vessey@xxxxxxxxxx>, "Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>, "Subrahmanian, Raj" <raj.subrahmanian@xxxxxxxxxx>
Delivery-date: 2005年10月05日 22:07:57 +0000
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On 5 Oct 2005, at 22:46, Keir Fraser wrote:
Does anyone know if there are other places where the "lock" prefix is
used with a cache misaligned address?
x86 systems are supposed to guarantee that LOCKed instructions access their memory operand atomically, regardless of alignment (Vol 3 of the Intel reference manual). Your systems break this application-visible guarantee?
Also, the patch is way bigger and more invasive than it needs to be. There should be no need to make pfn_info bigger than it is. It's currently a multiple of 8 bytes (e.g., 24 bytes on 32-bit) which is sufficient to avoid cache-line crossing of aligned 8-byte quantities. What if we just move 'tlbflush_timestamp' to the end of the structure? A one-line fix? :-)
 -- Keir
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