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Fri, 27 Nov 2020 15:45:37 +0100 (CET) From: Markus Armbruster To: Claudio Fontana Subject: Re: [PATCH v2 2/6] accel: accel_available() function References: <20201125205636.3305257-1-ehabkost@redhat.com> <20201125205636.3305257-3-ehabkost@redhat.com> <12f82771-9db9-8fcd-ea25-736428d2650a@suse.de> <20201126133645.GG2271382@habkost.net> <8d90d611-6545-a478-1316-542dc5424b92@suse.de> <7df7713c-5125-9e41-3572-a476cad2946b@suse.de> <20201126214810.GR2271382@habkost.net> <55ed249f-9fd3-fe3d-c63a-8d74803a72ca@suse.de> Date: Fri, 27 Nov 2020 15:45:37 +0100 In-Reply-To: <55ed249f-9fd3-fe3d-c63a-8d74803a72ca@suse.de> (Claudio Fontana's message of "Fri, 27 Nov 2020 10:04:37 +0100") Message-ID: <87y2imq2ni.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , Eduardo Habkost , Richard Henderson , qemu-devel@nongnu.org, Roman Bolshakov , Gerd Hoffmann , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Claudio Fontana writes: > On 11/26/20 10:48 PM, Eduardo Habkost wrote: >> On Thu, Nov 26, 2020 at 10:06:03PM +0100, Claudio Fontana wrote: >>> On 11/26/20 3:25 PM, Paolo Bonzini wrote: >>>> On 26/11/20 15:13, Claudio Fontana wrote: >>>>> One option I see is simply to document the behavior where >>>>> accel_available() is declared in accel.h (ie do not use in fast >>>>> path), as well as in accel_find() actually, so that both accel_find() >>>>> and accel_available() are avoided in fast path and avoid being called >>>>> frequently at runtime. >>>>> >>>>> Another option could be to remove the allocation completely, and use >>>>> for example accel_find(ACCEL_CLASS_NAME("tcg")), or another option >>>>> again would be to remove the allocation and use either a fixed buffer >>>>> + snprintf, or alloca -like builtin code to use the stack, ... >>>>> >>>>> Not a big deal, but with a general utility and short name like >>>>> accel_available(name) it might be tempting to use this more in the >>>>> future? >>>> >>>> I think it's just that the usecase is not that common. "Is this >>>> accelerator compiled in the binary" is not something you need after >>>> startup (or if querying the monitor). >>>> >>>> Paolo >>>> >>>> >>> >>> A script that repeatedly uses the QMP interface to query for >>> the status could generate fragmentation this way I think. >> >> Is this a problem? Today, execution of a "query-kvm" command >> calls g_malloc() 37 times. >> > > Not ideal in my view, but not the end of the world either. QMP's appetite for malloc is roughly comparable to a pig's for truffles.