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

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Message-ID: <bd4114c2-a6d9-123c-8f9f-e6da33a481ba@arm.com>
Date:   Fri, 2 Dec 2016 09:35:10 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     "majun (Euler7)" <majun258@...wei.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:     dingtianhong@...wei.com, guohanjun@...wei.com
Subject: Re: [RFC PATCH 0/3] Add a new flag for ITS device to control indirect
 route

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?

>> 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.
-- 
Jazz is not dead. It just smells funny...