From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MhZqw-000665-Ml for qemu-devel@nongnu.org; Sat, 29 Aug 2009 22:09:10 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MhZqs-00065g-Km for qemu-devel@nongnu.org; Sat, 29 Aug 2009 22:09:10 -0400 Received: from [199.232.76.173] (port=50661 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MhZqs-00065a-Ai for qemu-devel@nongnu.org; Sat, 29 Aug 2009 22:09:06 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:47715) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MhZqr-0006Jw-Qc for qemu-devel@nongnu.org; Sat, 29 Aug 2009 22:09:06 -0400 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e38.co.us.ibm.com (8.14.3/8.13.1) with ESMTP id n7U25C9R012835 for ; Sat, 29 Aug 2009 20:05:12 -0600 Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id n7U28wUR210682 for ; Sat, 29 Aug 2009 20:08:58 -0600 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n7U28v4O012491 for ; Sat, 29 Aug 2009 20:08:58 -0600 Message-ID: <4A99DF70.4000202@us.ibm.com> Date: Sat, 29 Aug 2009 22:09:52 -0400 From: Beth Kon MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 2/2] Route IOAPIC interrupts via ISA bus References: <1249836296-13288-1-git-send-email-avi@redhat.com> <1249836296-13288-3-git-send-email-avi@redhat.com> <4A955CB4.4080205@redhat.com> <4A955D6A.9060804@redhat.com> <4A973EF1.10707@us.ibm.com> <4A9969C9.9020806@redhat.com> In-Reply-To: <4A9969C9.9020806@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Andriy Gapon , Gerd Hoffmann , qemu-devel@nongnu.org Avi Kivity wrote: > On 08/28/2009 05:20 AM, Beth Kon wrote: >> I was thinking of the HPET advertising one or more of these new >> ioapic interrupts so that it could support non-legacy operation. It >> can't at the moment because there are no interrupt lines available. I >> haven't looked into the details of what would remain to be done to >> make this happen, but does it sound reasonable? Sounds like at a >> minimum acpi needs some work. > > What does non-legacy HPET buy us? > Actually, it looks like not much. I was thinking about users of /dev/hpet, but there really don't seem to be any. I found posts talking about deprecating the hpet ioctl interface due to availability of POSIX timers, so it doesn't look like anything is on the horizon. Right now, linux has no HPET requirements that aren't handled by timers 0 and 1 that are currently implemented for qemu/kvm, and as far as I can tell, Windows has no such need either. But, to be precise, even if the HPET runs in legacy mode, the standard hardware implementation as I understand it has a third timer available that is not involved with legacy operation. Because there were no spare interrupts around, I recently submitted patches to remove that third timer (that doesn't appear to be used anywhere). When I saw the possible availability of more APIC interrupt lines, I thought about using that for at least this third timer. The above thoughts came about after Andriy Gapon brought up some issues with available HPET interrupts. Andriy, do you have anything to add here about potential use of a third timer or non-legacy mode? Right now I'm inclined to think there isn't much use, and limiting HPET to legacy mode would be fine.