Re: [Xen-devel] [RFC PATCH V4 11/18] Bump EVTCHNS_PER_BUCKET to 512

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 15/03/13 18:37, Wei Liu wrote:
> On Fri, 2013-03-15 at 18:15 +0000, David Vrabel wrote:
>> On 05/03/13 12:30, Wei Liu wrote:
>>> For 64 bit build and 3-level event channel and the original value of
>>> EVTCHNS_PER_BUCKET (128), the space needed to accommodate d->evtchn would 
>>> be 4
>>> pages (PAGE_SIZE = 4096). Given that not every domain needs 3-level event
>>> channel, this leads to waste of memory. Having EVTCHN_PER_BUCKETS to be 512
>>> can occupy exact one page.
>>
>> This makes the list of buckets a page in size but each bucket is now 4
>> pages.
>>
> 
> I'm confused.

3 pages (not 4) with flask, 2 pages without.

> On 64 bit w/ FLASK enabled, sizeof(struct evtchn) = 18B, bucket size =
> 9216B = 2.25 pages; w/o FLASK enabled, sizeof(struct evtchn) = 10B,
> bucket size = 5120B = 1.25 pages.

struct evtchn isn't packed so it is 24 bytes with flask and 16 without.

David

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