Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751652AbbGMOuJ (ORCPT ); Mon, 13 Jul 2015 10:50:09 -0400 Received: from mga02.intel.com ([134.134.136.20]:14640 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751247AbbGMOuH (ORCPT ); Mon, 13 Jul 2015 10:50:07 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,463,1432623600"; d="scan'208";a="746178588" Message-ID: <55A3CEF2.2030200@linux.intel.com> Date: Mon, 13 Jul 2015 22:45:06 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Paolo Bonzini , Alex Williamson CC: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR References: <1431499348-25188-1-git-send-email-guangrong.xiao@linux.intel.com> <1431499348-25188-2-git-send-email-guangrong.xiao@linux.intel.com> <1436722432.1391.347.camel@redhat.com> <55A2B8F7.1050805@linux.intel.com> <55A36976.6090807@redhat.com> In-Reply-To: <55A36976.6090807@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2016 Lines: 59 On 07/13/2015 03:32 PM, Paolo Bonzini wrote: >>> I'm seeing a significant regression in boot performance on Intel >>> hardware with assigned devices that bisects back to this patch. There's >>> a long delay with Seabios between the version splash and execution of >>> option ROMs, and a _very_ long delay with OVMF before the display is >>> initialized. The delay is long enough that users are reporting their >>> previously working VM is hung with 100% CPU usage on v4.2-rc1. Thanks, >>> >> >> Alex, thanks for your report. I will try to reproduce and fix it asap. > I have reproduced the issue and I think Bandan and Paolo is correct. > The code that Bandan pointed out > > + /* MTRR is completely disabled, use UC for all of physical memory. */ > + if (!(mtrr_state->enabled & 0x2)) > + return MTRR_TYPE_UNCACHABLE; > > actually disappears in commit fa61213746a7 (KVM: MTRR: simplify > kvm_mtrr_get_guest_memory_type, 2015-06-15). Should mtrr_default_type > actually be something like this: :( Based on the SDM, UC is applied to all memory rather than default-type if MTRR is disabled. If i changed the code to: if (!(mtrr_state->enabled & 0x2)) return mtrr_state->def_type; the result is the same as before. However, fast boot came back if "return 0xFF" here. So fast boot expects that the memory type is WB. > > static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state) > { > if (mtrr_is_enabled(mtrr_state)) > return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK; > else > return MTRR_TYPE_UNCACHABLE; > } > > ? Then it's easy to add a quirk that makes the default WRITEBACK until > MTRRs are enabled. It is the wrong configure in OVMF... shall we need to adjust KVM to satisfy OVMF? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/