From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=56653 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OLASq-0006sm-Rb for qemu-devel@nongnu.org; Sun, 06 Jun 2010 03:40:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OLASp-0001r4-MM for qemu-devel@nongnu.org; Sun, 06 Jun 2010 03:40:12 -0400 Received: from mail-px0-f173.google.com ([209.85.212.173]:57866) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OLASp-0001r0-Fu for qemu-devel@nongnu.org; Sun, 06 Jun 2010 03:40:11 -0400 Received: by pxi2 with SMTP id 2so842720pxi.4 for ; Sun, 06 Jun 2010 00:40:10 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100606071536.GA2337@redhat.com> References: <20100601183058.GB6191@redhat.com> <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> From: Blue Swirl Date: Sun, 6 Jun 2010 07:39:49 +0000 Message-ID: Subject: Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers with delivery feedback Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: Jan Kiszka , qemu-devel@nongnu.org, Juan Quintela On Sun, Jun 6, 2010 at 7:15 AM, 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 occur >> > 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 either >> > 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 { >> > =C2=A0DeviceState *src; >> > =C2=A0void (*delivery_cb)(IRQMsg *msg, int result); >> > =C2=A0void (*eoi_cb)(IRQMsg *msg, int result); >> > =C2=A0void *src_opaque; >> > =C2=A0void *payload; >> > }; >> >> Extending the lifetime of IRQMsg objects beyond the delivery call stack >> 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 case >> 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 elements: > 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 interrupt. > But ack notifiers actually has another use: device assignment. There is > a plan to move device assignment from kernel to userspace and for that > 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 registered > notifier based on irqchip/pin. Because translation at IOAPIC may be lossy, IRQs from many devices pointing to the same vector? With IRQMsg you know where a specific message came from. The situation is different inside the kernel: it manages both translation and registration, whereas in QEMU we could only control registration.