From: Julien Grall <julien.grall@linaro.org>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: stefano.stabellini@eu.citrix.com, tim@xen.org,
xen-devel@lists.xen.org, Roy Franz <roy.franz@linaro.org>,
Jan Beulich <JBeulich@suse.com>, Fu Wei <fu.wei@linaro.org>
Subject: Re: [PATCH RFC 2/2] xen: arm: Enable physical address space compression (PDX) on arm64
Date: Mon, 08 Sep 2014 17:32:05 -0700 [thread overview]
Message-ID: <540E4A85.3030404@linaro.org> (raw)
In-Reply-To: <1409848806.10156.44.camel@kazak.uk.xensource.com>
On 04/09/14 09:40, Ian Campbell wrote:
>> I don't really understand what the function is achieving. Could you
>> explain a bit more?
>
> This is largely derived from an x86 equivalent (see srat_parse_regions,
> they are different because one walks the device tree RAM and the other
> the SRAT), so I hope Jan will correct me if I'm wrong about the
> following:
>
> What it is doing is calculating a mask which corresponds to to the bits
> that are active address bits across the valid memory addresses, i.e. a
> bit which is necessary to unambiguously represent some valid address is
> 1 and a bit which is the same for all addresses is 0.
>
> Using that mask we then find a large run of zeroes from he middle of the
> mask which by construction do not actually get used for addressing. By
> omitting those bits from the PFN we obtain a PDX which is the
> (losslessly) compressed form.
Many thank for the explanation!
--
Julien Grall
next prev parent reply other threads:[~2014-09-09 0:32 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <a0063c96455a2512091f40df5b7b8ec5bbef4b13.1406804493.git.ian.campbell@citrix.com>
2014-07-31 11:01 ` [PATCH RFC 2/2] xen: arm: Enable physical address space compression (PDX) on arm64 Ian Campbell
[not found] ` <53da2211.8511ec0a.4375.46ddSMTPIN_ADDED_MISSING@mx.google.com>
2014-08-06 3:04 ` Roy Franz
2014-08-07 16:03 ` Julien Grall
2014-09-04 16:40 ` Ian Campbell
2014-09-05 8:20 ` Jan Beulich
2014-09-05 8:26 ` Ian Campbell
2014-09-09 0:32 ` Julien Grall [this message]
2014-09-09 12:16 ` Ian Campbell
2014-09-09 16:54 ` Roy Franz
2014-09-09 20:59 ` Julien Grall
2014-09-10 9:36 ` Ian Campbell
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