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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF2DFC004D4 for ; Fri, 20 Jan 2023 01:12:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229958AbjATBMC (ORCPT ); Thu, 19 Jan 2023 20:12:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36548 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229583AbjATBMA (ORCPT ); Thu, 19 Jan 2023 20:12:00 -0500 Received: from mail-pf1-x42e.google.com (mail-pf1-x42e.google.com [IPv6:2607:f8b0:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B06A4DBE2 for ; Thu, 19 Jan 2023 17:11:59 -0800 (PST) Received: by mail-pf1-x42e.google.com with SMTP id i1so2890257pfk.3 for ; Thu, 19 Jan 2023 17:11:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=KLLOuv1S5xTn1rjXYscOd3PZw73M1sWaf11TFHQjeg8=; b=oc7HVVLv88ufQU5NguQWqr8Yr0B+TbXhg3pHSzEF3mb1513AIEvN+qVrl93YRQjYTi JZPwF2tZVOQ0WA5KVzRKqwyqSZJE6bERKsncHfxssopTBFL3Rr28s343sD9KmnDt1ec6 N8MHya73KVh3JsGmouPFO9RdobrdGOLt+nSG4hXI+DN8Yjz48Mka8QQeLqTAM9VdN/OS LldSrQ3e5IniqwA7PZ1T1c1mubkhdWVT1fYdx4xwpWsFI+2YQ75JjDIvZRcJRcEa/7ol UUwHH/M6Nl/H+tlIDND9uRJNZEWj2VVUmhiqzGcHaFTHdVvUu5s1XoxuVzQFxC/C15Fp EycA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=KLLOuv1S5xTn1rjXYscOd3PZw73M1sWaf11TFHQjeg8=; b=nmZC6Md9mEc+8782u2ox2jRzQ46ke3IPsOWGdQMpj39HmcvcrcgBnWbBHwi0FpuqLi v2QWV3/gR9k4TL+rBQHAo1/r5/nj0vv4qLS7hbzY3Fp3N/6Oq1PJh6NdD3Uh33YUsOR8 AWVjswrFAL1abNR+oLC1xbOnp6JwfzkOBHI1cahuAAzEEgjn0pysBoULe2uPiDKw6/iH YUt0L6+/nRoDoSbfX3qoTQ2ZJ57PqZyVUVDxy9kB1OS5584IkcBHRjOHzX7BKabVSBaB lbm2u0CoEh3B+Oicb/clw7+H2Q+jBwLSC5Pib1hmggNW9Isv97vylx0fK/AFDOHsUXOG Xb0Q== X-Gm-Message-State: AFqh2kqVqW8CsyEz7gzYzdN9rRgYHu2bDuIfcCNZNSoOGEHnPUqW5Say knxupDHAZ9sELis8Uuc/jBNawg== X-Google-Smtp-Source: AMrXdXtsYDh4XwQKTw1fk+Yq+6SQ99wH8Qs5JDgrnN4pwtbfObWS2/M+QfH5uPvgXUrSV2Ay0gYgfA== X-Received: by 2002:aa7:8692:0:b0:582:13b5:d735 with SMTP id d18-20020aa78692000000b0058213b5d735mr18721pfo.0.1674177118583; Thu, 19 Jan 2023 17:11:58 -0800 (PST) Received: from google.com (7.104.168.34.bc.googleusercontent.com. [34.168.104.7]) by smtp.gmail.com with ESMTPSA id k18-20020a628412000000b0058103f45d9esm21477938pfd.82.2023.01.19.17.11.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 17:11:58 -0800 (PST) Date: Fri, 20 Jan 2023 01:11:54 +0000 From: Sean Christopherson To: Like Xu Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 8/8] KVM: x86/cpuid: Use fast return for cpuid "0xa" leaf when !enable_pmu Message-ID: References: <20221111102645.82001-1-likexu@tencent.com> <20221111102645.82001-9-likexu@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221111102645.82001-9-likexu@tencent.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 11, 2022, Like Xu wrote: > From: Like Xu > > Although when !enable_pmu, KVM will have zero-padded kvm_pmu_cap to do > subsequent cpuid leaf assignments, one extra branch instruction saves > a few subsequent zero-assignment instructions, speeding things up a bit. I doubt my motivation was performance, I'm guessing I suggested adding the explicit !enable_pmu check because relying on kvm_pmu_cap to be zeroed isn't obvious.