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Message-ID: <abb15757-cbe6-037f-e8d3-5df9fbbf6c04@huawei.com>
Date: Thu, 26 Oct 2023 09:55:39 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: Mark Rutland <mark.rutland@....com>
CC: <broonie@...nel.org>, <joey.gouly@....com>, <will@...nel.org>,
<amit.kachhap@....com>, <rafael@...nel.org>,
<catalin.marinas@....com>, <james.morse@....com>, <maz@...nel.org>,
<viresh.kumar@...aro.org>, <sumitg@...dia.com>,
<yang@...amperecomputing.com>, <linux-kernel@...r.kernel.org>,
<linux-pm@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
<wangxiongfeng2@...wei.com>, <xiexiuqi@...wei.com>,
Ionela Voinescu <ionela.voinescu@....com>
Subject: Re: [PATCH 3/3] cpufreq: CPPC: Eliminate the impact of cpc_read()
latency error
在 2023/10/25 19:01, Mark Rutland 写道:
> On Wed, Oct 25, 2023 at 05:38:47PM +0800, Zeng Heng wrote:
>
> The previous patch added this function, and calls it with smp_call_on_cpu(),
> where it'll run in IRQ context with IRQs disabled...
smp_call_on_cpu() puts the work to the bind-cpu worker.
And this function will be called in task context, and IRQs is certainly enabled.
Zeng Heng
>> struct fb_ctr_pair *fb_ctrs = val;
>> int cpu = fb_ctrs->cpu;
>> int ret;
>> + unsigned long timeout;
>>
>> ret = cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t0);
>> if (ret)
>> return ret;
>>
>> - udelay(2); /* 2usec delay between sampling */
>> + if (likely(!irqs_disabled())) {
>> + /*
>> + * Set 1ms as sampling interval, but never schedule
>> + * to the idle task to prevent the AMU counters from
>> + * stopping working.
>> + */
>> + timeout = jiffies + msecs_to_jiffies(1);
>> + while (!time_after(jiffies, timeout))
>> + cond_resched();
>> +
>> + } else {
> ... so we'll enter this branch of the if-else ...
>
>> + pr_warn_once("CPU%d: Get rate in atomic context", cpu);
> ... and pr_warn_once() for something that's apparently normal and outside of
> the user's control?
>
> That doesn't make much sense to me.
>
> Mark.
>
>> + udelay(2); /* 2usec delay between sampling */
>> + }
>>
>> return cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t1);
>> }
>> --
>> 2.25.1
>>
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