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Message-ID: <88780123-32a3-ab34-cd3d-01e4a3421f03@quicinc.com>
Date: Tue, 14 Jun 2022 19:44:27 +0530
From: Neeraj Upadhyay <quic_neeraju@...cinc.com>
To: "zhangfei.gao@...mail.com" <zhangfei.gao@...mail.com>,
Shameerali Kolothum Thodi
<shameerali.kolothum.thodi@...wei.com>,
"paulmck@...nel.org" <paulmck@...nel.org>
CC: Paolo Bonzini <pbonzini@...hat.com>,
Zhangfei Gao <zhangfei.gao@...aro.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"rcu@...r.kernel.org" <rcu@...r.kernel.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Josh Triplett <josh@...htriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Matthew Wilcox <willy@...radead.org>,
"mtosatti@...hat.com" <mtosatti@...hat.com>,
Auger Eric <eric.auger@...hat.com>,
"chenxiang (M)" <chenxiang66@...ilicon.com>
Subject: Re: Commit 282d8998e997 (srcu: Prevent expedited GPs and blocking
readers from consuming CPU) cause qemu boot slow
On 6/14/2022 7:33 PM, zhangfei.gao@...mail.com wrote:
>
>
> On 2022/6/14 下午8:19, Neeraj Upadhyay wrote:
>>
>>>
>>> 5.18-rc4 based ~8sec
>>>
>>> 5.19-rc1 ~2m43sec
>>>
>>> 5.19-rc1+fix1 ~19sec
>>>
>>> 5.19-rc1-fix2 ~19sec
>>>
>>
>> If you try below diff on top of either 5.19-rc1+fix1 or 5.19-rc1-fix2
>> ; does it show any difference in boot time?
>>
>> --- a/kernel/rcu/srcutree.c
>> +++ b/kernel/rcu/srcutree.c
>> @@ -706,7 +706,7 @@ static void srcu_schedule_cbs_snp(struct
>> srcu_struct *ssp, struct srcu_node *snp
>> */
>> static void srcu_gp_end(struct srcu_struct *ssp)
>> {
>> - unsigned long cbdelay;
>> + unsigned long cbdelay = 1;
>> bool cbs;
>> bool last_lvl;
>> int cpu;
>> @@ -726,7 +726,9 @@ static void srcu_gp_end(struct srcu_struct *ssp)
>> spin_lock_irq_rcu_node(ssp);
>> idx = rcu_seq_state(ssp->srcu_gp_seq);
>> WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
>> - cbdelay = !!srcu_get_delay(ssp);
>> + if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq),
>> READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
>> + cbdelay = 0;
>> +
>> WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns());
>>
> Test here:
> qemu: https://github.com/qemu/qemu/tree/stable-6.1
> kernel:
> https://github.com/Linaro/linux-kernel-uadk/tree/uacce-devel-5.19-srcu-test
> (in case test patch not clear, push in git tree)
>
> Hardware: aarch64
>
> 1. 5.18-rc6
> real 0m8.402s
> user 0m3.015s
> sys 0m1.102s
>
> 2. 5.19-rc1
> real 2m41.433s
> user 0m3.097s
> sys 0m1.177s
>
> 3. 5.19-rc1 + fix1 from Paul
> real 2m43.404s
> user 0m2.880s
> sys 0m1.214s
>
> 4. 5.19-rc1 + fix2: fix1 + Remove "if (!jbase)" block
> real 0m15.262s
> user 0m3.003s
> sys 0m1.033s
>
> When build kernel in the meantime, load time become longer.
>
> 5. 5.19-rc1 + fix3: fix1 + SRCU_MAX_NODELAY_PHASE 1000000
> real 0m15.215s
> user 0m2.942s
> sys 0m1.172s
>
> 6. 5.19-rc1 + fix4: fix1 + Neeraj's change of srcu_gp_end
> real 1m23.936s
> user 0m2.969s
> sys 0m1.181s
>
Thanks for this data. Can you please share below test combo also?
7. 5.19-rc1 + fix5: fix2 + Neeraj's change of srcu_gp_end
8. 5.19-rc1 + fix6: fix3 + Neeraj's change of srcu_gp_end
Thanks
Neeraj
> More test details: https://docs.qq.com/doc/DRXdKalFPTVlUbFN5
>
> Thanks
>
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