linux-kernel - Re: [PATCH v1 2/2] scsi: ufs: disable interrupt during clock-gating

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Date:   Wed, 18 Dec 2019 15:37:26 -0800
From:   "Asutosh Das (asd)" <asutoshd@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        avri.altman@....com, alim.akhtar@...sung.com,
        pedrom.sousa@...opsys.com, jejb@...ux.ibm.com,
        matthias.bgg@...il.com, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        beanhuo@...ron.com, kuohong.wang@...iatek.com,
        peter.wang@...iatek.com, chun-hung.wu@...iatek.com,
        andy.teng@...iatek.com
Subject: Re: [PATCH v1 2/2] scsi: ufs: disable interrupt during clock-gating

On 12/17/2019 7:52 PM, Stanley Chu wrote:
> Hi Asutosh,
> 
> On Tue, 2019-12-17 at 15:25 -0800, Asutosh Das (asd) wrote:
>>>
>>
>> Hi,
>> Does this save significant power? I see that gate/ungate of clocks
>> happen far too frequently than suspend/resume.
>>
>> Have you considered how much latency this would add to the
>> gating/ungating path?
>>
>> -asd
>>
> 
> Yes, we have measured 200 times clk-gating/clk-ungating and latency data
> is showed as below,
> 
> For clk-gating with interrupt disabling toggled,
> 
> 	Average latency of each clk-gating: 55.117 us
> 	Average latency of irq-disabling during clk-gating: 4.2 us
> 
> For clk-ungating with interrupt enabling toggled,
> 	Average latency of each clk-ungating: 118.324 us
> 	Average latency of irq-enabling during clk-ungating: 2.9 us
> 
> The evaluation here is based on below Can's patch therefore the
> interrupt control (enable_irq/disable_irq) latency is much shorter than
> before (request_irq/free_irq).
> 
> scsi: ufs: Do not free irq in suspend
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/scsi/ufs/ufshcd.c?id=8709c1f68536e256668812788af5b2bb027f49c3
> 
> BTW, the main purpose of this patch is aimed to protect ufshcd register
> from accessing while host clocks are disabled to fix potential system
> hang issue. The possible scenario is mentioned in commit message of
> patch "scsi: ufs: disable irq before disabling clocks" in the same
> series.
> 
> Thanks
> Stanley
> 

Reviewed-by: Asutosh Das <asutoshd@...eaurora.org>

Thanks for the data.
It'd be interesting to know more on the - misrouted interrupt recovery 
feature though.

-
Thanks
Asutosh

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