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 7B315EB64D9 for ; Wed, 14 Jun 2023 11:16:33 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1q9OTg-0001Pz-8c; Wed, 14 Jun 2023 07:15:52 -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 1q9OTe-0001PR-7S for qemu-devel@nongnu.org; Wed, 14 Jun 2023 07:15:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1q9OTc-00083p-K5 for qemu-devel@nongnu.org; Wed, 14 Jun 2023 07:15:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686741347; 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=+qMRXwWzTqDuizTjkfKiVrvMTBT5b/GwJ9j3B741FxQ=; b=M8iiQgKPY1hBL8ScIpjySTnFLFzZ5s8uXYylhXsGovVpBwN63+z5HB56m9cW8Omrq6nZ96 IM595v5Hc203ipqYaNS1oqU7RwP1rwPgu5zCHlcNGecvHZghVZ3DSwqczxFh69WbGOy0Nw 5EhdgxHyMFs9/nMwHK5yac6ZmvtWf9M= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-321-GLBmhLOWNMGRphUwcYoGfg-1; Wed, 14 Jun 2023 07:15:46 -0400 X-MC-Unique: GLBmhLOWNMGRphUwcYoGfg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7FCD3185A78B; Wed, 14 Jun 2023 11:15:45 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.170]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5D4AA40C20F4; Wed, 14 Jun 2023 11:15:45 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 3B8FB21E668A; Wed, 14 Jun 2023 13:15:44 +0200 (CEST) From: Markus Armbruster To: Marcelo Tosatti Cc: qemu-devel , Paolo Bonzini , Mark Kanda Subject: Re: [PATCH] kvm: reuse per-vcpu stats fd to avoid vcpu interruption References: Date: Wed, 14 Jun 2023 13:15:44 +0200 In-Reply-To: (Marcelo Tosatti's message of "Tue, 13 Jun 2023 15:22:41 -0300") Message-ID: <87h6rab8gv.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.129.124; 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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Marcelo Tosatti writes: > A regression has been detected in latency testing of KVM guests. > More specifically, it was observed that the cyclictest > numbers inside of an isolated vcpu (running on isolated pcpu) are: > > # Max Latencies: 00090 00096 00141 > > Where a maximum of 50us is acceptable. > > The implementation of KVM_GET_STATS_FD uses run_on_cpu to query > per vcpu statistics, which interrupts the vcpu (and is unnecessary). > > To fix this, open the per vcpu stats fd on vcpu initialization, > and read from that fd from QEMU's main thread. > > Signed-off-by: Marcelo Tosatti [...] > @@ -4038,7 +4040,8 @@ static StatsDescriptors *find_stats_descriptors(StatsTarget target, int stats_fd > } > > static void query_stats(StatsResultList **result, StatsTarget target, > - strList *names, int stats_fd, Error **errp) > + strList *names, int stats_fd, Error **errp, > + CPUState *cpu) include/qapi/error.h: * - Functions that use Error to report errors have an Error **errp * parameter. It should be the last parameter, except for functions * taking variable arguments. > { > struct kvm_stats_desc *kvm_stats_desc; > struct kvm_stats_header *kvm_stats_header; [...]