From: Keir Fraser <keir.xen@gmail.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Daniel De Graaf <dgdegra@tycho.nsa.gov>,
David Vrabel <david.vrabel@citrix.com>,
xen-devel@lists.xen.org
Subject: Re: [PATCH v2] xen/evtchn: rearrange fields
Date: Tue, 01 Apr 2014 16:56:53 +0100 [thread overview]
Message-ID: <533AE1C5.5030208@gmail.com> (raw)
In-Reply-To: <5332CB110200007800002456@nat28.tlf.novell.com>
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Jan Beulich wrote:
>>>> On 25.03.14 at 18:23,<dgdegra@tycho.nsa.gov> wrote:
>> > Event channel arrays are allocated in blocks with EVTCHNS_PER_BUCKET
>> > elements, which must be a power of 2. When XSM is disabled, struct
>> > evtchn is 32 bytes including padding; however, when XSM is enabled, the
>> > structure becomes larger and EVTCHNS_PER_BUCKET is halved. Rearranging
>> > some of the fields in struct evtchn allows a 4-byte XSM field to fit
>> > within the 32-byte structure.
>> >
>> > This rearrangement turns the xen_consumer field of struct evtchn into a
>> > bitfield and adjusts the xen_consumers array to fit the number of
>> > addressable elements from this value. Since there are currently only
>> > two users of this array, only 3 bits (7 values) are reserved. This
>> > field is also used rarely enough that the slight overhead from applying
>> > a bitmask should not cause problems.
>> >
>> > Signed-off-by: Daniel De Graaf<dgdegra@tycho.nsa.gov>
>> > Cc: David Vrabel<david.vrabel@citrix.com>
>
> Reviewed-by: Jan Beulich<jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
>
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prev parent reply other threads:[~2014-04-01 15:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-25 17:23 [PATCH v2] xen/evtchn: rearrange fields Daniel De Graaf
2014-03-26 11:41 ` Jan Beulich
2014-04-01 15:56 ` Keir Fraser [this message]
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