linux-kernel - Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests send/compl paths

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Message-ID: <adc85803e27226bc8d24c53061e39214@codeaurora.org>
Date:   Wed, 02 Jun 2021 10:14:39 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bean Huo <huobean@...il.com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, Stanley Chu <stanley.chu@...iatek.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v1 2/3] scsi: ufs: Optimize host lock on transfer requests
 send/compl paths

Hi Bean,

On 2021-06-01 00:04, Bean Huo wrote:
> On Mon, 2021-05-24 at 01:36 -0700, Can Guo wrote:
>> Current UFS IRQ handler is completely wrapped by host lock, and
>> because
>> 
>> ufshcd_send_command() is also protected by host lock, when IRQ
>> handler
>> 
>> fires, not only the CPU running the IRQ handler cannot send new
>> requests,
>> 
>> the rest CPUs can neither. Move the host lock wrapping the IRQ
>> handler into
>> 
>> specific branches, i.e., ufshcd_uic_cmd_compl(),
>> ufshcd_check_errors(),
>> 
>> ufshcd_tmc_handler() and ufshcd_transfer_req_compl(). Meanwhile, to
>> further
>> 
>> reduce occpuation of host lock in ufshcd_transfer_req_compl(), host
>> lock is
>> 
>> no longer required to call __ufshcd_transfer_req_compl(). As per
>> test, the
>> 
>> optimization can bring considerable gain to random read/write
>> performance.
>> 
>> 
>> 
>> Cc: Stanley Chu <stanley.chu@...iatek.com>
>> 
>> Co-developed-by: Asutosh Das <asutoshd@...eaurora.org>
>> 
>> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
>> 
>> Signed-off-by: Can Guo <cang@...eaurora.org>
> 
> Can,
> The patch looks good to me.
> I did a UFS queue limitation test before, observed that once the queue
> is full, then the active task number in the queue will get down. For
> the Nvme, the scenario is the same. You can refer to the slide 23, and
> slide 24 in the pdf:
> https://elinux.org/images/6/6c/Linux_Storage_System_Bottleneck_Exploration_V0.3.pdf
> I don't know if your patch can fix this
> issue.

I've studied these slides made by you many times, it is really good.
I will do some study later on this. Thanks for the slides.

> 
> Unfortunately, I cannot verify UTRLCNR usage flow since my platform is
> v2.1. But at least my test can prove that the patch doesn't impact the
> legacy(UFSHCI is less than v3.0) doorbell usage flow.
> 

Thanks for your time :).

Regards,
Can Guo.

> Reviewed-by: Bean Huo <beanhuo@...ron.com>
> 
> 
> Bean