linux-kernel - Re: [RFC PATCH] mmc: core: Disable REQ_FUA if the eMMC supports an internal cache

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Message-ID: <58bb34de-e333-00bd-ae3f-4ddf0e56aa5d@gmail.com>
Date:   Thu, 2 Mar 2023 16:02:26 +0100
From:   Bean Huo <huobean@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Cc:     Wenchao Chen <wenchao.chen666@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Avri Altman <avri.altman@....com>,
        Christian Lohle <cloehle@...erstone.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mmc: core: Disable REQ_FUA if the eMMC supports an
 internal cache

On 02.03.23 3:43 PM, Ulf Hansson wrote:
> REQ_FUA is in general supported for eMMC cards, which translates into so
> called "reliable writes". To support these write operations, the CMD23
> (MMC_CAP_CMD23), needs to be supported by the mmc host too, which is common
> but not always the case.
>
> For some eMMC devices, it has been reported that reliable writes are quite
> costly, leading to performance degradations.
>
> In a way to improve the situation, let's avoid announcing REQ_FUA support
> if the eMMC supports an internal cache, as that allows us to rely solely on
> flush-requests (REQ_OP_FLUSH) instead, which seems to be a lot cheaper.
> Note that, those mmc hosts that lacks CMD23 support are already using this
> type of configuration, whatever that could mean.
>
> Reported-by: Wenchao Chen<wenchao.chen666@...il.com>
> Signed-off-by: Ulf Hansson<ulf.hansson@...aro.org>
Acked-by: Bean Huo <beanhuo@...ron.com>