From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9A5F9C3DA7F for ; Wed, 31 Jul 2024 08:43:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sZ4v9-0007jh-3y; Wed, 31 Jul 2024 04:42:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZ4v8-0007ga-Bv for qemu-devel@nongnu.org; Wed, 31 Jul 2024 04:42:54 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZ4v6-0003XD-RM for qemu-devel@nongnu.org; Wed, 31 Jul 2024 04:42:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722415372; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=6s7ClsJ2DKLcy/84CoFLT/gUrVMTGlM5VvNrcIpjRRY=; b=GNIP87UMZRDLlgklcIoU8z0MyH80el+tQJRwX5SUX0AsnZ5P6ZSiz6W+Twiku3I4EyxL77 geoRZs0OlHr8va1Od5u+gmZ2aCzHmSqSZ364Mv7aijTMHiNOLCfBNlwmmfttdGsuaERTqi uxCv/fiO90vbECvejMP6uHnvqNW/wXM= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-160-EgeKoRbaOwGaJZmTEiw40w-1; Wed, 31 Jul 2024 04:42:47 -0400 X-MC-Unique: EgeKoRbaOwGaJZmTEiw40w-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E2FE719560BF; Wed, 31 Jul 2024 08:42:45 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.65]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8E45B19560AA; Wed, 31 Jul 2024 08:42:45 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 5BEDB21E6690; Wed, 31 Jul 2024 10:42:43 +0200 (CEST) From: Markus Armbruster To: Andrew Jones Cc: Daniel Henrique Barboza , qemu-devel@nongnu.org, pbonzini@redhat.com, richard.henderson@linaro.org, berrange@redhat.com, eduardo@habkost.net Subject: Re: [PATCH v2 2/2] qom/object, accel-system: add support to Accel globals In-Reply-To: <20240731-b34061e3e3d7ce4c3d76f481@orel> (Andrew Jones's message of "Wed, 31 Jul 2024 09:41:39 +0200") References: <20240703204149.1957136-1-dbarboza@ventanamicro.com> <20240703204149.1957136-3-dbarboza@ventanamicro.com> <87bk2ekr8p.fsf@pond.sub.org> <20240731-b34061e3e3d7ce4c3d76f481@orel> Date: Wed, 31 Jul 2024 10:42:43 +0200 Message-ID: <87ttg6hrzw.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.125, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Andrew Jones writes: > On Wed, Jul 31, 2024 at 08:30:46AM GMT, Markus Armbruster wrote: >> I apologize for the delay. >> >> Daniel Henrique Barboza writes: >> >> > We're not honouring KVM options that are provided by any -accel option >> > aside from the first. In this example: >> > >> > qemu-system-riscv64 -accel kvm,riscv-aia=emul (...) \ >> > -accel kvm,riscv-aia=hwaccel >> > >> > 'riscv-aia' will be set to 'emul', ignoring the last occurrence of the >> > option that set 'riscv-aia' to 'hwaccel'. >> >> The way you phrase this, it sounds like a bug. But as far as I know, >> -accel is meant to have fallback semantics: we use the first one that >> works. > > The fact that some (most?) parameters have override semantics and some > have fallback semantics makes our complicated command line even more > complicated, especially since there's no way to know which is which. We traditionally tramsmit such knowledge from guru to disciple. We certainly made an unholy mess of our command line. > IMHO, always having override semantics and then providing new parameters, > e.g. -accel-fallback (or a property, -accel fallback=on,...), would go a > long way to bringing some order to the universe. > >> Perhaps: >> >> -accel has fallback semantics, i.e. we try accelerators in order until >> we find one that works. Any remainder is ignored. >> >> Because of that, you can't override properties like this: >> >> qemu-system-riscv64 -accel kvm,riscv-aia=emul (...) \ >> -accel kvm,riscv-aia=hwaccel >> >> When KVM is available, 'riscv-aia' will be set to 'emul', and the >> second -accel is ignored. When KVM is not available, neither option >> works, and the command fails. >> >> Why would you want to override accelerator properties? > > Testing. Many properties are only available to allow the user to force > non defaults. The example above isn't exactly what triggered this. The > real use is, '-accel kvm' is the default used by libvirt and when > riscv-aia=hwaccel is possible, it will default to hwaccel. In order to > test riscv-aia emulation support using libvirt (which doesn't yet allow > selecting anything riscv specific), I attempted to use the qemu > commandline element to override -accel with kvm,riscv-aia=emul. Ah, that explains why -global solves your problem, too! Thanks! I recommend to start the commit message with the use case, then describe the solution. Mention other solutions last, if at all.