linux-kernel - Re: [PATCH v2 1/3] scsi: ufs: core: Introduce mcq ops to config cqid

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Date:   Thu, 1 Jun 2023 10:25:59 +0000
From:   Powen Kao (高伯文) <Powen.Kao@...iatek.com>
To:     "bvanassche@....org" <bvanassche@....org>,
        "chu.stanley@...il.com" <chu.stanley@...il.com>
CC:     Peter Wang (王信友) 
        <peter.wang@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        CC Chou (周志杰) <cc.chou@...iatek.com>,
        Eddie Huang (黃智傑) 
        <eddie.huang@...iatek.com>,
        Alice Chao (趙珮均) 
        <Alice.Chao@...iatek.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "avri.altman@....com" <avri.altman@....com>,
        Chun-Hung Wu (巫駿宏) 
        <Chun-hung.Wu@...iatek.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        Naomi Chu (朱詠田) <Naomi.Chu@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Stanley Chu (朱原陞) 
        <stanley.chu@...iatek.com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v2 1/3] scsi: ufs: core: Introduce mcq ops to config cqid

On Wed, 2023-05-31 at 05:48 -0700, Bart Van Assche wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On 5/30/23 18:54, Stanley Chu wrote:
> > In addition, some benchmark data shows that the performance can be
> > improved by using fewer CQs to aggregate the interrupt handling of
> > completion requests.
> 
> What has been measured? IOPS only or both IOPS and latency?
> 
> How big is the difference? A few percent or more?
> For which number of SQs and which number of CQs has performance data 
> been measured?
> 
Comparing 8-8 to 8-1 mapping, it shows few percents improvement.

> 
> Would the following work instead of introducing a new vop?
> - Introduce a new capability flag, e.g. UFSHCD_CAP_SINGLE_CQ.
> - Set that flag from inside ufs_mtk_init().
> - Modify the UFS core driver such that the number of completion
> queues
>    depends on the UFSHCD_CAP_SINGLE_CQ flag.
> 
According to spec, driver is free to assign any SQ to CQ mapping. I am
not sure if it's ideal to constrain mapping to specific kind.

> > Therefore, we would like to introduce a vop to allow the host to
> > configure it accordingly.
> 
> We do not accept new vops upstream without a user. Where is the 
> implementation of the new .config_cqid() callback?
> 

Yes, please refer to
"[PATCH v2 3/3] scsi: ufs: ufs-mediatek: Add MCQ support for MTK
platform"

+static int ufs_mtk_config_cqid(struct ufs_hba *hba)
+{
+       struct ufs_hw_queue *hwq;
+       int i;
+
+       for (i = 0; i < hba->nr_hw_queues; i++) {
+               hwq = &hba->uhq[i];
+               hwq->cqid = 3;
+       }
+
+       return 0;
+}


Po-Wen