linux-kernel - Re: [PATCH v6 0/5] scsi: ufs: Add Host Performance Booster Support

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Date:   Wed, 22 Jul 2020 09:27:07 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Daejun Park <daejun7.park@...sung.com>,
        "avri.altman@....com" <avri.altman@....com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "bvanassche@....org" <bvanassche@....org>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>
Subject: Re: [PATCH v6 0/5] scsi: ufs: Add Host Performance Booster Support


Christoph,

> As this monster seesm to come back again and again let me re-iterate
> my statement:
>
> I do not think Linux should support a broken standards extensions that
> creates a huge share state between the Linux initator and the target
> device like this with all its associated problems.

I spent a couple of hours looking at this series again last night. And
while the code has improved, I do remain concerned about the general
concept.

I understand how caching the FTL in host memory can improve performance
from a theoretical perspective. However, I am not sure how much a
difference this is going to make outside of synthetic benchmarks. What
are the workloads that keep reading the same blocks from media? Or does
the performance improvement exclusively come from the second order
pre-fetching effect for larger I/Os? If so, why is the device's internal
L2P SRAM cache ineffective at handling that case?

-- 
Martin K. Petersen	Oracle Linux Engineering