linux-kernel - Re: [PATCH] f2fs: add sysfs entry to avoid FUA

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Message-ID: <YpZ3WI/Vjgk/CwFE@google.com>
Date:   Tue, 31 May 2022 13:15:20 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-block@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH] f2fs: add sysfs entry to avoid FUA

On 05/27, Christoph Hellwig wrote:
> On Fri, May 27, 2022 at 06:06:08PM -0700, Jaegeuk Kim wrote:
> > I think there's still some benefit to use FUA such as small chunk writes
> > for checkpoint.
> 
> Did you measure if there is?  Because some SSDs basically implemented
> FUA as an implied flush after the write, in which case it would not
> really help there either (but also not hurt).
> 
> But as the previous two maintainers already said - this needs quirking
> at the driver layer, not in the submitter.

Thanks, I indeed measured this using UFS, and it turned out cache_flush
is better than FUA all the time like this. Hence, I posted a quirk [1].

Write(us/KB)	4	64	256	1024	2048
FUA		873.792	754.604	995.624	1011.67	1067.99
CACHE_FLUSH	824.703	712.98	800.307	1019.5	1037.37

[1] https://lore.kernel.org/linux-scsi/20220531201053.3300018-1-jaegeuk@kernel.org/T/#u