From: Zdenek Kaspar <zkaspar82@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: Bad performance since 5.9-rc1
Date: Tue, 12 Jan 2021 12:18:11 +0100 [thread overview]
Message-ID: <20210112121811.408e32fe.zkaspar82@gmail.com> (raw)
In-Reply-To: <20201222222645.0d8e96b2.zkaspar82@gmail.com>
On Tue, 22 Dec 2020 22:26:45 +0100
Zdenek Kaspar <zkaspar82@gmail.com> wrote:
> On Tue, 22 Dec 2020 09:07:39 -0800
> Sean Christopherson <seanjc@google.com> wrote:
>
> > On Mon, Dec 21, 2020, Zdenek Kaspar wrote:
> > > [ 179.364305] WARNING: CPU: 0 PID: 369 at
> > > kvm_mmu_zap_oldest_mmu_pages+0xd1/0xe0 [kvm] [ 179.365415] Call
> > > Trace: [ 179.365443] paging64_page_fault+0x244/0x8e0 [kvm]
> >
> > This means the shadow page zapping is occuring because KVM is
> > hitting the max number of allowed MMU shadow pages. Can you
> > provide your QEMU command line? I can reproduce the performance
> > degredation, but only by deliberately overriding the max number of
> > MMU pages via `-machine kvm-shadow-mem` to be an absurdly low value.
> >
> > > [ 179.365596] kvm_mmu_page_fault+0x376/0x550 [kvm]
> > > [ 179.365725] kvm_arch_vcpu_ioctl_run+0xbaf/0x18f0 [kvm]
> > > [ 179.365772] kvm_vcpu_ioctl+0x203/0x520 [kvm]
> > > [ 179.365938] __x64_sys_ioctl+0x338/0x720
> > > [ 179.365992] do_syscall_64+0x33/0x40
> > > [ 179.366013] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> It's one long line, added "\" for mail readability:
>
> qemu-system-x86_64 -machine type=q35,accel=kvm \
> -cpu host,host-cache-info=on -smp cpus=2,cores=2 \
> -m size=1024 -global virtio-pci.disable-legacy=on \
> -global virtio-pci.disable-modern=off \
> -device virtio-balloon \
> -device virtio-net,netdev=tap-build,mac=DE:AD:BE:EF:00:80 \
> -object rng-random,filename=/dev/urandom,id=rng0 \
> -device virtio-rng,rng=rng0 \
> -name build,process=qemu-build \
> -drive
> file=/mnt/data/export/unix/kvm/build/openbsd-amd64.img,if=virtio,cache=none,format=raw,aio=native
> \ -netdev type=tap,id=tap-build,vhost=on \ -serial
> none \ -parallel none
> \ -monitor
> unix:/dev/shm/kvm-build.sock,server,nowait \ -enable-kvm
> -daemonize -runas qemu
>
> Z.
BTW, v5.11-rc3 with kvm-shadow-mem=1073741824 it seems OK.
Just curious what v5.8 does, so by any chance is there command
for kvm-shadow-mem value via qemu monitor?
Z.
next prev parent reply other threads:[~2021-01-12 11:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 3:05 Bad performance since 5.9-rc1 Zdenek Kaspar
2020-12-01 6:35 ` Zdenek Kaspar
2020-12-18 19:33 ` Zdenek Kaspar
2020-12-21 19:41 ` Sean Christopherson
2020-12-21 21:13 ` Zdenek Kaspar
2020-12-22 17:07 ` Sean Christopherson
2020-12-22 21:26 ` Zdenek Kaspar
2021-01-12 11:18 ` Zdenek Kaspar [this message]
2021-01-13 20:17 ` Sean Christopherson
2021-01-13 22:17 ` Zdenek Kaspar
2020-12-02 0:31 ` Sean Christopherson
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