From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=54450 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OLAth-0001Cx-RU for qemu-devel@nongnu.org; Sun, 06 Jun 2010 04:07:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OLAtf-0004UH-Ob for qemu-devel@nongnu.org; Sun, 06 Jun 2010 04:07:56 -0400 Received: from fmmailgate02.web.de ([217.72.192.227]:49430) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OLAtf-0004U4-Ai for qemu-devel@nongnu.org; Sun, 06 Jun 2010 04:07:55 -0400 Message-ID: <4C0B5754.9090707@web.de> Date: Sun, 06 Jun 2010 10:07:48 +0200 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers with delivery feedback References: <4C074A72.3070507@web.de> <20100603063456.GM24302@redhat.com> <4C0752CB.9030701@web.de> <20100603070300.GN24302@redhat.com> <20100603070559.GO24302@redhat.com> <4C099471.3060507@web.de> <20100606071536.GA2337@redhat.com> <4C0B5098.8030800@web.de> <20100606074934.GD2337@redhat.com> In-Reply-To: <20100606074934.GD2337@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig5DCDAA383B09D68332A9689F" Sender: jan.kiszka@web.de List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: Blue Swirl , qemu-devel@nongnu.org, Juan Quintela This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig5DCDAA383B09D68332A9689F Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Gleb Natapov wrote: > On Sun, Jun 06, 2010 at 09:39:04AM +0200, Jan Kiszka wrote: >> Gleb Natapov wrote: >>> On Sat, Jun 05, 2010 at 02:04:01AM +0200, Jan Kiszka wrote: >>>>> I'd like to also support EOI handling. When the guest clears the >>>>> interrupt condtion, the EOI callback would be called. This could oc= cur >>>>> much later than the IRQ delivery time. I'm not sure if we need the >>>>> result code in that case. >>>>> >>>>> If any intermediate device (IOAPIC?) needs to be informed about eit= her >>>>> delivery or EOI also, it could create a proxy message with its >>>>> callbacks in place. But we need then a separate opaque field (in >>>>> addition to payload) to store the original message. >>>>> >>>>> struct IRQMsg { >>>>> DeviceState *src; >>>>> void (*delivery_cb)(IRQMsg *msg, int result); >>>>> void (*eoi_cb)(IRQMsg *msg, int result); >>>>> void *src_opaque; >>>>> void *payload; >>>>> }; >>>> Extending the lifetime of IRQMsg objects beyond the delivery call st= ack >>>> means qemu_malloc/free for every delivery. I think it takes a _very_= >>>> appealing reason to justify this. But so far I do not see any use ca= se >>>> for eio_cb at all. >>>> >>> I dislike use of eoi for reinfecting missing interrupts since >>> it eliminates use of internal PIC/APIC queue of not yet delivered >>> interrupts. PIC and APIC has internal queue that can handle two eleme= nts: >>> one is delivered, but not yet acked interrupt in isr and another is >>> pending interrupt in irr. Using eoi callback (or ack notifier as it's= >>> called inside kernel) interrupt will be considered coalesced even if = irr >>> is cleared, but no ack was received for previously delivered interrup= t. >>> But ack notifiers actually has another use: device assignment. There = is >>> a plan to move device assignment from kernel to userspace and for tha= t >>> ack notifiers will have to be extended to userspace too. If so we can= >>> use them to do irq decoalescing as well. I doubt they should be part >>> of IRQMsg though. Why not do what kernel does: have globally register= ed >>> notifier based on irqchip/pin. >> I read this twice but I still don't get your plan. Do you like or >> dislike using EIO for de-coalescing? And how should these notifiers wo= rk? >> > That's because I confused myself :) I _dislike_ them to be used, but > since device assignment requires ack notifiers anyway may be it is bett= er > to introduce one mechanism for device assignmen + de-coalescing instead= > of introducing two different mechanism. Using ack notifiers should be > easy: RTC registers ack notifier and keep track of delivered interrupts= =2E > If timer triggers after previews irq was set, but before it was acked > coalesced counter is incremented. In ack notifier callback coalesced > counter is checked and if it is not zero new irq is set. Ack notifier registrations and event deliveries still need to be routed. Piggy-backing this on IRQ messages may be unavoidable for that reason. Anyway, I'm going to post my HPET updates with the infrastructure for IRQMsg now. Maybe it's helpful to see the other option in reality. Jan --------------enig5DCDAA383B09D68332A9689F Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkwLV1cACgkQitSsb3rl5xRU2QCgzFgQ+rvGNJWgv5iLs+2ik/j0 USgAoIBsddjaH6GGjvq9L34xffS2MwN/ =hZaS -----END PGP SIGNATURE----- --------------enig5DCDAA383B09D68332A9689F--