linux-kernel - RE: [PATCH V2 0/2] mmc: block: Support Host to control FUA

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Message-ID: <0a9cf24cb65d49838c95455bb54ebf10@hyperstone.com>
Date:   Fri, 21 Oct 2022 16:32:39 +0000
From:   Christian Löhle <CLoehle@...erstone.com>
To:     Christian Löhle <CLoehle@...erstone.com>,
        "Wenchao Chen" <wenchao.chen666@...il.com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "orsonzhai@...il.com" <orsonzhai@...il.com>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        "zhang.lyra@...il.com" <zhang.lyra@...il.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "avri.altman@....com" <avri.altman@....com>,
        "kch@...dia.com" <kch@...dia.com>
CC:     "vincent.whitchurch@...s.com" <vincent.whitchurch@...s.com>,
        "bigeasy@...utronix.de" <bigeasy@...utronix.de>,
        "s.shtylyov@....ru" <s.shtylyov@....ru>,
        "michael@...winnertech.com" <michael@...winnertech.com>,
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        "megoo.tang@...il.com" <megoo.tang@...il.com>,
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Subject: RE: [PATCH V2 0/2] mmc: block: Support Host to control FUA


> 
> Unless there is something special / wrong with sdhci-sprd (unlikely? Its just a flag) or your eMMC (maybe more likely?) then Id expect this or similar performance degradation for any host controller and eMMC.
> I can redo some measurement if you provide your workload.
> But I'd say if you don’t want to pay the price of reliable write then make sure to not issue them, by not issuing FUA?
> Maybe I'm misunderstanding, but why would the host controller driver control FUA?
> 

Maybe one more point on that: Compare performance with fua disabled but cache off, should be comparable unless there is an actual reliable write problem.
If reliable write is performing horribly on that eMMC maybe a quirk could be thought of.
Anyway your 13MB/s random with fua, if a reliable write is basically always active for a given cache size,
doesn't sound totally unreasonable (over 3000 IOPS, assuming 4k writes).

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