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Subject: Re: Commit 282d8998e997 (srcu: Prevent expedited GPs and blocking
 readers from consuming CPU) cause qemu boot slow
To:     paulmck@kernel.org, Zhangfei Gao <zhangfei.gao@linaro.org>
Cc:     "linux-kernel@vger.kernel.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>
References: <20615615-0013-5adc-584f-2b1d5c03ebfc@linaro.org>
 <20220611165956.GO1790663@paulmck-ThinkPad-P17-Gen-1>
From:   "zhangfei.gao@foxmail.com" <zhangfei.gao@foxmail.com>
Date:   Sun, 12 Jun 2022 15:40:30 +0800
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Hi, Paul

On 2022/6/12 上午12:59, Paul E. McKenney wrote:
> On Sun, Jun 12, 2022 at 12:32:59AM +0800, Zhangfei Gao wrote:
>> Hi, Paul
>>
>> When verifying qemu with acpi rmr feature on v5.19-rc1, the guest kernel
>> stuck for several minutes.
> Stuck for several minutes but then continues normally?  Or stuck for
> several minutes before you kill qemu?
qemu boot stuck for several minutes, then guest can bootup normally, 
just slower.
>
> And I have to ask...  What happened without the ACPI RMR feature?
If no ACPI, qemu boot quickly without stuck.
build/aarch64-softmmu/qemu-system-aarch64 -machine 
virt,gic-version=3,iommu=smmuv3 \
-enable-kvm -cpu host -m 1024 \
-kernel Image -initrd mini-rootfs.cpio.gz -nographic -append \
"rdinit=init console=ttyAMA0 earlycon=pl011,0x9000000 kpti=off"

Adding acpi=force & -bios QEMU_EFI.fd, qemu boot stuck for several minutes.


By the way, my hardware platform is aarch64.

Only change this can solve the stuck issue.

--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -524,6 +524,10 @@ static unsigned long srcu_get_delay(struct 
srcu_struct *ssp)
  {
         unsigned long jbase = SRCU_INTERVAL;

+       if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), 
READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
+               return 0;
+       return SRCU_INTERVAL;
+

>
>> And on 5.18, there is no such problem.
>>
>> After revert this patch, the issue solved.
>> Commit 282d8998e997 (srcu: Prevent expedited GPs and blocking readers from
>> consuming CPU)
>>
>>
>> qemu cmd:
>> build/aarch64-softmmu/qemu-system-aarch64 -machine
>> virt,gic-version=3,iommu=smmuv3 \
>> -enable-kvm -cpu host -m 1024 \
>> -kernel Image -initrd mini-rootfs.cpio.gz -nographic -append \
>> "rdinit=init console=ttyAMA0 earlycon=pl011,0x9000000 kpti=off acpi=force" \
>> -bios QEMU_EFI.fd
>>
>> log:
>> InstallProtocolInterface: 5B1B31A1-9562-11D2-8E3F-00A0C969723B 7AA4D040
>> add-symbol-file /home/linaro/work/edk2/Build/ArmVirtQemu-AARCH64/DEBUG_GCC48/AARCH64/NetworkPkg/IScsiDxe/IScsiDxe/DEBUG/IScsiDxe.dll
>> 0x75459000
>> Loading driver at 0x00075458000 EntryPoint=0x00075459058 IScsiDxe.efi
>> InstallProtocolInterface: BC62157E-3E33-4FEC-9920-2D3B36D750DF 7AA4DE98
>> ProtectUefiImageCommon - 0x7AA4D040
>>    - 0x0000000075458000 - 0x000000000003F000
>> SetUefiImageMemoryAttributes - 0x0000000075458000 - 0x0000000000001000
>> (0x0000000000004008)
>> SetUefiImageMemoryAttributes - 0x0000000075459000 - 0x000000000003B000
>> (0x0000000000020008)
>> SetUefiImageMemoryAttributes - 0x0000000075494000 - 0x0000000000003000
>> (0x0000000000004008)
>> InstallProtocolInterface: 18A031AB-B443-4D1A-A5C0-0C09261E9F71 754952C8
>> InstallProtocolInterface: 107A772C-D5E1-11D4-9A46-0090273FC14D 75495358
>> InstallProtocolInterface: 6A7A5CFF-E8D9-4F70-BADA-75AB3025CE14 75495370
>> InstallProtocolInterface: 18A031AB-B443-4D1A-A5C0-0C09261E9F71 754952F8
>> InstallProtocolInterface: 107A772C-D5E1-11D4-9A46-0090273FC14D 75495358
>> InstallProtocolInterface: 6A7A5CFF-E8D9-4F70-BADA-75AB3025CE14 75495370
>> InstallProtocolInterface: 59324945-EC44-4C0D-B1CD-9DB139DF070C 75495348
>> InstallProtocolInterface: 09576E91-6D3F-11D2-8E39-00A0C969723B 754953E8
>> InstallProtocolInterface: 330D4706-F2A0-4E4F-A369-B66FA8D54385 7AA4D728
>>
>>
>> Not sure it is either reported or solved.
> This is the first I have heard of it, so thank you for reporting it.
>
> Do you have a way of collecting something sysrq-t output?
Do you mean "echo t > /proc/sysrq-trigger",
There are too much output and kernel dump can not stop.

Thanks