From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=45573 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OGnfy-0006Uw-TO for qemu-devel@nongnu.org; Tue, 25 May 2010 02:31:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OGnfx-0002J1-2Z for qemu-devel@nongnu.org; Tue, 25 May 2010 02:31:42 -0400 Received: from fmmailgate03.web.de ([217.72.192.234]:48699) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OGnfw-0002In-KY for qemu-devel@nongnu.org; Tue, 25 May 2010 02:31:41 -0400 Message-ID: <4BFB6EAA.40803@web.de> Date: Tue, 25 May 2010 08:31:06 +0200 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers with delivery feedback References: <20100525060715.GN22163@redhat.com> In-Reply-To: <20100525060715.GN22163@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig1B8BE34C6876940D4F1F08E5" 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) --------------enig1B8BE34C6876940D4F1F08E5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Gleb Natapov wrote: > On Mon, May 24, 2010 at 10:13:40PM +0200, Jan Kiszka wrote: >> From: Jan Kiszka >> >> This allows to communicate potential IRQ coalescing during delivery fr= om >> the sink back to the source. Targets that support IRQ coalescing >> workarounds need to register handlers that return the appropriate >> QEMU_IRQ_* code, and they have to propergate the code across all IRQ >> redirections. If the IRQ source receives a QEMU_IRQ_COALESCED, it can >> apply its workaround. If multiple sinks exist, the source may only >> consider an IRQ coalesced if all other sinks either report >> QEMU_IRQ_COALESCED as well or QEMU_IRQ_MASKED. >> > Well, almost two years passed since this approach was proposed first > time[1] ;). Back then it generated bunch of nonsensical comments about > real hardware not working this way, so the hack that we have now was > introduce to overcome this resistance. I hope enough time passed for > people to gain some sense and the approach will be adopted this time. > Really this should have been done two year ago. >=20 > [1] http://lists.nongnu.org/archive/html/qemu-devel/2008-06/msg00757.ht= ml Yeah, I somehow had a vague feeling that there must have been an earlier attempt. I think my approach could be a slightly easier to accept as it does not require converting all platforms, but this can happen on demand (or not at all). Moreover, I think that the third return state, QEMU_IRQ_MASKED, is important for correct handling of multiple IRQ sinks.= However, as I would see it now, we just have two options long term: - drop IRQ coalescing workarounds - properly support them via qemu_irq The current hack cannot stay. E.g., it does not scale because it depends on a global variable of the APIC. So we would never able to protect the APICs with individual locks. Jan --------------enig1B8BE34C6876940D4F1F08E5 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 iEYEARECAAYFAkv7bq4ACgkQitSsb3rl5xSjdQCeOBhF2dYk+r0uso4ocib8iWdp +JgAnjd/RTuf1gUO7NgkM30nOEpucKBF =aujt -----END PGP SIGNATURE----- --------------enig1B8BE34C6876940D4F1F08E5--