Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 15 Jun 2022 09:38:34 +0100
Message-ID: <871qvq48z9.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Cc:     "zhangfei.gao@foxmail.com" <zhangfei.gao@foxmail.com>,
        "paulmck@kernel.org" <paulmck@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Zhangfei Gao <zhangfei.gao@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Matthew Wilcox <willy@infradead.org>,
        "mtosatti@redhat.com" <mtosatti@redhat.com>,
        Auger Eric <eric.auger@redhat.com>,
        "chenxiang (M)" <chenxiang66@hisilicon.com>
Subject: Re: Commit 282d8998e997 (srcu: Prevent expedited GPs and blocking readers from consuming CPU) cause qemu boot slow
In-Reply-To: <110bbec5cee74efba0aad64360069a12@huawei.com>
References: <20220611165956.GO1790663@paulmck-ThinkPad-P17-Gen-1>
        <tencent_80D2801BC03B7006BB2230B6A1D5C69B9209@qq.com>
        <20220612133631.GQ1790663@paulmck-ThinkPad-P17-Gen-1>
        <tencent_2B7B5B8DBE69330DA041AEE36C1029826905@qq.com>
        <20220612162029.GR1790663@paulmck-ThinkPad-P17-Gen-1>
        <20220612164002.GA1242564@paulmck-ThinkPad-P17-Gen-1>
        <560f7d27-fe38-0db9-834a-50dda5fa6157@redhat.com>
        <20220612184944.GU1790663@paulmck-ThinkPad-P17-Gen-1>
        <tencent_E306F58EAEC1D188ED6D5F358A269F34C707@qq.com>
        <20220613035711.GY1790663@paulmck-ThinkPad-P17-Gen-1>
        <20220613041652.GA3976000@paulmck-ThinkPad-P17-Gen-1>
        <tencent_F82250B6E3D51A9AC0D2BE1AE43A4E060909@qq.com>
        <110bbec5cee74efba0aad64360069a12@huawei.com>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue)
 FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1
 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

On Mon, 13 Jun 2022 16:02:30 +0100,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com> wrote:
> 
> 
> 
> > -----Original Message-----
> > From: zhangfei.gao@foxmail.com [mailto:zhangfei.gao@foxmail.com]
> > Sent: 13 June 2022 07:56
> > To: paulmck@kernel.org
> > Cc: Paolo Bonzini <pbonzini@redhat.com>; Zhangfei Gao
> > <zhangfei.gao@linaro.org>; linux-kernel@vger.kernel.org;
> > rcu@vger.kernel.org; Lai Jiangshan <jiangshanlai@gmail.com>; Josh Triplett
> > <josh@joshtriplett.org>; Mathieu Desnoyers
> > <mathieu.desnoyers@efficios.com>; Matthew Wilcox <willy@infradead.org>;
> > Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> > mtosatti@redhat.com; Auger Eric <eric.auger@redhat.com>
> > Subject: Re: Commit 282d8998e997 (srcu: Prevent expedited GPs and
> > blocking readers from consuming CPU) cause qemu boot slow
> > 
>  
> > By the way, the issue should be only related with qemu apci. not related
> > with rmr feature
> > Test with: https://github.com/qemu/qemu/tree/stable-6.1
> > 
> > Looks it caused by too many kvm_region_add & kvm_region_del if
> > acpi=force,
> 
> Based on the setup I have, I think it has nothing to do with Guest
> kernel booting with ACPI per se(ie, acpi=force in Qemu kernel cmd
> line).  It is more to do with Qemu having the "-bios QEMU_EFI.fd"
> which sets up pflash devices resulting in large number of pflash
> read/write calls(before Guest kernel even boots) which in turn seems
> to be triggering the below kvm_region_add/del calls.

Indeed, this is all about memslots being added/removed at an alarming
rate (well, not more alarming today than yesterday, but QEMU's flash
emulation is... interesting).

	M.

-- 
Without deviation from the norm, progress is not possible.