linux-kernel - Re: [RFC PATCH 0/3] Add a new flag for ITS device to control indirect route

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Date:   Mon, 5 Dec 2016 11:11:28 +0800
From:   "majun (Euler7)" <majun258@...wei.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        <linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
        <robert.moore@...el.com>, <lenb@...nel.org>, <lv.zheng@...el.com>,
        <rafael.j.wysocki@...el.com>, <devel@...ica.org>,
        <mark.rutland@....com>, <robh+dt@...nel.org>,
        <jason@...edaemon.net>
CC:     <majun258@...wei.com>, <dingtianhong@...wei.com>,
        <guohanjun@...wei.com>
Subject: Re: [RFC PATCH 0/3] Add a new flag for ITS device to control indirect
 route

Hi Marc:

在 2016/12/2 17:35, Marc Zyngier 写道:
> On 02/12/16 09:29, majun (Euler7) wrote:
>>
>>
>> 在 2016/12/1 17:07, Marc Zyngier 写道:
>>> On 01/12/16 07:45, Majun wrote:
>>>> From: MaJun <majun258@...wei.com>
>>>>
>>>> For current ITS driver, two level table (indirect route) is enabled when the memory used
>>>> for LPI route table over the limit(64KB * 2) size. But this function impact the 
>>>> performance of LPI interrupt actually because need more time to look up the table.
>>>
>>> Are you implying that your ITS doesn't have a cache to lookup the most
>>> active devices, hence performing a full lookup on each interrupt?
>>
>> Our ITS chip has the cache with depth 64. But this seems not enough for some
>> scenario,espeically on virtulization platform.
> 
> Then I don't see how switching to to flat tables is going to improve
> things. Can you share actual performance numbers?
> 
Sorry, I run this code on EMU and have no actual performance numbers now.

Suppose there are 66 devices in system.
As far as our chip concerned, there are always 2 devices can't benefit from
cache fully when they report the interrupt.

If i'm wrong, please correct me.

Thanks
Majun

>>> Anyway, doing this as a DT quirk doesn't feel right. Please use the ITS
>>> quirk infrastructure.
>>
>> If there is no other better solutions, I will do this.
> 
> Thanks,
> 
> 	M.
>