From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v4 05/17] xen/arm: ITS: implement hw_irq_controller for LPIs Date: Wed, 15 Jul 2015 11:49:09 +0200 Message-ID: <55A62C95.3040903@citrix.com> References: <1436514172-3263-1-git-send-email-vijay.kilari@gmail.com> <1436514172-3263-6-git-send-email-vijay.kilari@gmail.com> <55A42B1C.2030600@citrix.com> <55A61940.9010408@citrix.com> <1436952729.11153.28.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1436952729.11153.28.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Vijay Kilari , Stefano Stabellini , Prasun Kapoor , Vijaya Kumar K , Tim Deegan , "xen-devel@lists.xen.org" , Stefano Stabellini , manish.jaggi@caviumnetworks.com List-Id: xen-devel@lists.xenproject.org Hi Ian, On 15/07/2015 11:32, Ian Campbell wrote: >>>> Why can't we store the event ID in the irq_guest? As said on v3, this is not >>> >>> Are you referring to irq_desc in above statement? >> >> Yes sorry. > > I'm afraid I don't follow your suggestion here, are you suggesting that > the vid field added above should be moved to irq_desc? Yes, > But the vid _is_ domain specific, it is the virtual event ID which is > per-domain (it's the thing looked up in the ITT to get a vLPI to be > injected). I think it is a pretty direct analogue of the virq field used > for non-LPI irq_guest structs. No, vid is not specific to a domain but a device. The virtual event ID is always the same as the physical event ID (See your design document [1]). Furthermore, all the usage of the irq_to_vid in this series are for physical command (see lpi_set_config within this patch). > > Your proposal on v3 looks to be around moving the its_device pointer to > the irq_desc, which appears to have been done here, along with turning > the virq+vid into a union as requested there too. On v3 I said: "The event ID and the its_device assigned are known when the device is added to Xen and hence can be set in irq_desc (with a small memory impact, but we have plenty of memory on ARM64)." Sorry if it was confusing. > >>>> It has been suggested by Ian to move col_id in the its_device in the >>>> previous version [4]. Any reason to not doing it? >>> >>> In round robin fashion each plpi is attached to col_id. So storing >>> in its_device is not possible. In linux latest col_id is stored in its_device >>> structure for which set_affinity is called. > > Are you saying that in Linux all Events/LPIs associated with a given ITS > device are routed to the same collection? > >> You could do round robin on its_device... It would be exactly the same > > Routing all LPIs associated with a given its_device to the same > collection is not exactly the same as round robin-ing all LPIs from the > device over the collections. Yes, sorry I was a bit lax on the writing. I wanted to meant that there is not much difference to do it. >> and save 2 byte if not more with the alignment per irq_desc. > > If this is a concern then I would say we would either want a separate > array of per-pLPI information which we do not want in irq_desc because > it is irq specific, or do add a pointer to its_desc which points to an > array of per-event information. That would be a good solution. Although, as I said, I don't really care for Xen 4.6. It's more an optimization for 4.7. Regards, [1] http://xenbits.xen.org/people/ianc/vits/draftG.html#event-id-event -- Julien Grall