From: "lihuisong (C)" <lihuisong@huawei.com>
To: "Morten Brørup" <mb@smartsharesystems.com>, dev@dpdk.org
Cc: <thomas@monjalon.net>, <ferruh.yigit@amd.com>,
<anatoly.burakov@intel.com>, <david.hunt@intel.com>,
<sivaprasad.tummala@amd.com>, <liuyonglong@huawei.com>
Subject: Re: [PATCH 0/2] introduce PM QoS interface
Date: Tue, 26 Mar 2024 20:15:17 +0800 [thread overview]
Message-ID: <1e227884-348c-25eb-24c5-8ce19137173d@huawei.com> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F32E@smartserver.smartshare.dk>
在 2024/3/26 16:27, Morten Brørup 写道:
>> From: lihuisong (C) [mailto:lihuisong@huawei.com]
>> Sent: Tuesday, 26 March 2024 03.12
>>
>> 在 2024/3/22 20:35, Morten Brørup 写道:
>>>> From: lihuisong (C) [mailto:lihuisong@huawei.com]
>>>> Sent: Friday, 22 March 2024 09.54
> [...]
>
>>>> For the case need PM QoS in DPDK, I think, it is better to set cpu
>>>> latency to zero to prevent service thread from the deeper the idle
>> state.
>>> It would defeat the purpose (i.e. not saving sufficient amounts of
>> power) if the CPU cannot enter a deeper idle state.
>> Yes, it is not good for power.
>> AFAIS, PM QoS is just to decrease the influence for performance.
>> Anyway, if we set to zero, system can be into Cstates-0 at least.
>>> Personally, I would think a wake-up latency of up to 10 microseconds
>> should be fine for must purposes.
>>> Default Linux timerslack is 50 microseconds, so you could also use
>> that value.
>> How much CPU latency is ok. Maybe, we can give the decision to the
>> application.
> Yes, the application should decide the acceptable worst-case latency.
>
>> Linux will collect all these QoS request and use the minimum latency.
>> what do you think, Morten?
> For the example application, you could use a value of 50 microseconds and refer to this value also being the default timerslack in Linux.
There is a description for "/proc/<pid>/timerslack_ns" in Linux document [1]
"
This file provides the value of the task’s timerslack value in nanoseconds.
This value specifies an amount of time that normal timers may be
deferred in order to coalesce timers and avoid unnecessary wakeups.
This allows a task’s interactivity vs power consumption tradeoff to be
adjusted.
"
I cannot understand what the relationship is between the timerslack in
Linux and cpu latency to wake up.
It seems that timerslack is just to defer the timer in order to coalesce
timers and avoid unnecessary wakeups.
And it has not a lot to do with the CPU latency which is aimed to avoid
task to enter deeper idle state and satify application request.
>
next prev parent reply other threads:[~2024-03-26 12:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-20 10:55 Huisong Li
2024-03-20 10:55 ` [PATCH 1/2] power: " Huisong Li
2024-03-20 10:55 ` [PATCH 2/2] examples/l3fwd-power: add PM QoS request configuration Huisong Li
2024-03-20 14:05 ` [PATCH 0/2] introduce PM QoS interface Morten Brørup
2024-03-21 3:04 ` lihuisong (C)
2024-03-21 13:30 ` Morten Brørup
2024-03-22 8:54 ` lihuisong (C)
2024-03-22 12:35 ` Morten Brørup
2024-03-26 2:11 ` lihuisong (C)
2024-03-26 8:27 ` Morten Brørup
2024-03-26 12:15 ` lihuisong (C) [this message]
2024-03-26 12:46 ` Morten Brørup
2024-03-29 1:59 ` lihuisong (C)
2024-03-22 17:55 ` Tyler Retzlaff
2024-03-26 2:20 ` lihuisong (C)
2024-03-26 16:04 ` Tyler Retzlaff
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